At the basic premise, sensible gun control legislation isn't going to last because one side is more invested than the other. Those supporting the right to keep and bear arms, and the associated protections enshrined in the Second Amendment, see efforts that would restrict their ability to freely exercise their rights as an attack on the same. The opposition, motivated by emotions and sad thoughts, lack permanence. The side feeling aggressed will mount a stronger defense.
Second Amendment
The foundation of the argument for those supporting the individual right to keep and bear arms is the protection of the same enshrined in the Second Amendment. The text is quite clear, and attempts to create confusion or massage it into a restriction are efforts of obfuscation.:
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
Disaggregated into the individual clauses, translated into plain language into how they would have been understood at ratification:
A well regulated : in proper working order, being proficient
Militia : all able-bodied men who are not members of the Uniformed Services.
being necessary to the security of a free State : a nondespotically governed country
the right of the people : Individual Right
keep and bear Arms : the ability to have and carry arms.
shall not be infringed : The Federal and State Governments do not have the authority to violate the individual right to Keep and Bear Arms
Historic Context
What was the meaning of the Second Amendment as understood by its contemporaries? Was the aim about keeping weapons in your home while not having to be part of the response service (NG, Army)?
From a sister stack exchange, History.se, we have the following:
The historical context shows that it intends that everyone be armed, both for the defense of the state and for their own personal use; that the "militia" is intended to consist of all capable adults; that broad membership and independence from a centralized army is the very thing that makes it "well-regulated"; that people were afraid of the federal government raising an army that out-gunned the general populace; that an armed populace was considered a bulwark for other individual rights, to the point of being used as a defense against the government if it should ever take a turn to the tyrannical; and that the right to be armed was widely considered a natural right on a par with free speech, a free press, etc. A few quotes from contemporary writings:
Congress shall never disarm any Citizen unless such as are or have been in Actual Rebellion.
— The Constitutional convention of New Hampshire, in their proposed amendments to the Constitution.
That the people have the right to bear arms for the defence of the State; and, as standing armies, in time of peace, are dangerous to liberty, they ought not to be kept up; and that the military should be kept under the strict subordination to, and governed by, the civil power.
— North Carolina Constitution of 1776 (Section 30 in the linked version, except the last sentence there wasn't present in 1776). Similar language is also found in the minutes of the constitutional ratifying conventions of Virginia and New York.
And that the said Constitution be never construed to authorize Congress to infringe the just liberty of the press, or the rights of conscience; or to prevent the people of the United States, who are peaceable citizens, from keeping their own arms
— Samuel Adams, in the Constitutional convention of Massachusetts.
There are other things so clearly out of the power of Congress, that the bare recital of them is sufficient. I mean "the rights of conscience, of religious liberty — the rights of bearing arms for defence, or for killing game — the liberty of fowling, hunting, and fishing..." These things seem to have been inserted among their objections, merely to induce the ignorant to believe that Congress would have a power over such objects, and to infer from their being refused a place in the Constitution, their intention to exercise that power to the oppression of the people.
— Alexander White, in a response to a minority (anti-federalist) opinion of the constitutional convention of Pennsylvania. The minority opinion said that the Constitution was insufficient because it didn't protect individual rights well enough (i.e. they wanted a Bill of Rights baked into the Constitution). White says that such protection is unnecessary because it's blindingly obvious that the federal government has no right or power to curb those rights, even without their being listed specifically in the Constitution.
If the representatives of the people betray their constituents, there is then no recourse left but in the exertion of that original right of self-defense which is paramount to all positive forms of government
— Alexander Hamilton, Federalist no. 28
If circumstances should at any time oblige the government to form an army of any magnitude that army can never be formidable to the liberties of the people while there is a large body of citizens, little, if at all, inferior to them in discipline and the use of arms, who stand ready to defend their own rights and those of their fellow-citizens. This appears to me the only substitute that can be devised for a standing army, and the best possible security against it, if it should exist.
— Alexander Hamilton, Federalist no. 29
What, sir, is the use of a militia? It is to prevent the establishment of a standing army, the bane of liberty [...] Whenever governments mean to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise an army upon their ruins.
— Elbridge Gerry, House of Representatives debate on the adoption of the Bill of Rights. (He later became the original Gerrymanderer.)
"A free people ought not only to be armed, but disciplined..."
- George Washington, First Annual Address, to both House of Congress, January 8, 1790
"No free man shall ever be debarred the use of arms."
- Thomas Jefferson, Virginia Constitution, Draft 1, 1776
"I prefer dangerous freedom over peaceful slavery."
- Thomas Jefferson, letter to James Madison, January 30, 1787
"What country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance. Let them take arms."
- Thomas Jefferson, letter to James Madison, December 20, 1787
"The laws that forbid the carrying of arms are laws of such a nature. They disarm only those who are neither inclined nor determined to commit crimes.... Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man."
- Thomas Jefferson, Commonplace Book (quoting 18th century criminologist Cesare Beccaria), 1774-1776
"A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise and independence to the mind. Games played with the ball, and others of that nature, are too violent for the body and stamp no character on the mind. Let your gun therefore be your constant companion of your walks." - Thomas Jefferson, letter to Peter Carr, August 19, 1785
"The Constitution of most of our states (and of the United States) assert that all power is inherent in the people; that they may exercise it by themselves; that it is their right and duty to be at all times armed."
- Thomas Jefferson, letter to to John Cartwright, 5 June 1824
"On every occasion [of Constitutional interpretation] let us carry ourselves back to the time when the Constitution was adopted, recollect the spirit manifested in the debates, and instead of trying [to force] what meaning may be squeezed out of the text, or invented against it, [instead let us] conform to the probable one in which it was passed."
- Thomas Jefferson, letter to William Johnson, 12 June 1823
"I enclose you a list of the killed, wounded, and captives of the enemy from the commencement of hostilities at Lexington in April, 1775, until November, 1777, since which there has been no event of any consequence ... I think that upon the whole it has been about one half the number lost by them, in some instances more, but in others less. This difference is ascribed to our superiority in taking aim when we fire; every soldier in our army having been intimate with his gun from his infancy."
- Thomas Jefferson, letter to Giovanni Fabbroni, June 8, 1778
“They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
- Benjamin Franklin, Historical Review of Pennsylvania, 1759
"To disarm the people...[i]s the most effectual way to enslave them."
- George Mason, referencing advice given to the British Parliament by Pennsylvania governor Sir William Keith, The Debates in the Several State Conventions on the Adooption of the Federal Constitution, June 14, 1788
"I ask who are the militia? They consist now of the whole people, except a few public officers."
- George Mason, Address to the Virginia Ratifying Convention, June 4, 1788
"Before a standing army can rule, the people must be disarmed, as they are in almost every country in Europe. The supreme power in America cannot enforce unjust laws by the sword; because the whole body of the people are armed, and constitute a force superior to any band of regular troops."
- Noah Webster, An Examination of the Leading Principles of the Federal Constitution, October 10, 1787
"Besides the advantage of being armed, which the Americans possess over the people of almost every other nation, the existence of subordinate governments, to which the people are attached, and by which the militia officers are appointed, forms a barrier against the enterprises of ambition, more insurmountable than any which a simple government of any form can admit of."
- James Madison, Federalist No. 46, January 29, 1788
"The right of the people to keep and bear arms shall not be infringed. A well regulated militia, composed of the body of the people, trained to arms, is the best and most natural defense of a free country."
- James Madison, I Annals of Congress 434, June 8, 1789
"...the ultimate authority, wherever the derivative may be found, resides in the people alone..."
- James Madison, Federalist No. 46, January 29, 1788
"Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves."
- William Pitt (the Younger), Speech in the House of Commons, November 18, 1783
“A militia when properly formed are in fact the people themselves…and include, according to the past and general usuage of the states, all men capable of bearing arms… "To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them."
- Richard Henry Lee, Federal Farmer No. 18, January 25, 1788
"Guard with jealous attention the public liberty. Suspect everyone who approaches that jewel. Unfortunately, nothing will preserve it but downright force. Whenever you give up that force, you are ruined.... The great object is that every man be armed. Everyone who is able might have a gun."
- Patrick Henry, Speech to the Virginia Ratifying Convention, June 5, 1778
"This may be considered as the true palladium of liberty.... The right of self defense is the first law of nature: in most governments it has been the study of rulers to confine this right within the narrowest limits possible. Wherever standing armies are kept up, and the right of the people to keep and bear arms is, under any color or pretext whatsoever, prohibited, liberty, if not already annihilated, is on the brink of destruction."
- St. George Tucker, Blackstone's Commentaries on the Laws of England, 1803
"The supposed quietude of a good man allures the ruffian; while on the other hand, arms, like law, discourage and keep the invader and the plunderer in awe, and preserve order in the world as well as property. The balance ofpower is the scale of peace. The same balance would be preserved were all the world destitute of arms, for all would be alike; but since some will not, others dare not lay them aside. And while a single nation refuses to lay them down, it is proper that all should keep them up. Horrid mischief would ensue were one-half the world deprived of the use of them; for while avarice and ambition have a place in the heart of man, the weak will become a prey to the strong. The history of every age and nation establishes these truths, and facts need but little arguments when they prove themselves."
- Thomas Paine, "Thoughts on Defensive War" in Pennsylvania Magazine, July 1775
"The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms."
- Samuel Adams, Massachusetts Ratifying Convention, 1788
"The right of the citizens to keep and bear arms has justly been considered, as the palladium of the liberties of a republic; since it offers a strong moral check against the usurpation and arbitrary power of rulers; and will generally, even if these are successful in the first instance, enable the people to resist and triumph over them."
- Joseph Story, Commentaries on the Constitution of the United States, 1833
"What, Sir, is the use of a militia? It is to prevent the establishment of a standing army, the bane of liberty .... Whenever Governments mean to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise an army upon their ruins."
- Rep. Elbridge Gerry of Massachusetts, I Annals of Congress 750, August 17, 1789
"For it is a truth, which the experience of ages has attested, that the people are always most in danger when the means of injuring their rights are in the possession of those of whom they entertain the least suspicion."
- Alexander Hamilton, Federalist No. 25, December 21, 1787
"If the representatives of the people betray their constituents, there is then no resource left but in the exertion of that original right of self-defense which is paramount to all positive forms of government, and which against the usurpations of the national rulers, may be exerted with infinitely better prospect of success than against those of the rulers of an individual state. In a single state, if the persons intrusted with supreme power become usurpers, the different parcels, subdivisions, or districts of which it consists, having no distinct government in each, can take no regular measures for defense. The citizens must rush tumultuously to arms, without concert, without system, without resource; except in their courage and despair."
- Alexander Hamilton, Federalist No. 28
"[I]f circumstances should at any time oblige the government to form an army of any magnitude that army can never be formidable to the liberties of the people while there is a large body of citizens, little, if at all, inferior to them in discipline and the use of arms, who stand ready to defend their own rights and those of their fellow-citizens. This appears to me the only substitute that can be devised for a standing army, and the best possible security against it, if it should exist."
- Alexander Hamilton, Federalist No. 28, January 10, 1788
"As civil rulers, not having their duty to the people before them, may attempt to tyrannize, and as the military forces which must be occasionally raised to defend our country, might pervert their power to the injury of their fellow citizens, the people are confirmed by the article in their right to keep and bear their private arms."
- Tench Coxe, Philadelphia Federal Gazette, June 18, 1789
"A sword never kills anybody; it is a tool in the killer's hand."
- Lucius Annaeus Seneca
"I will teach my children weapons and warfare, so they might teach their children science and law, so they might teach their children art and literature."
- Unknown Greek
"Freedom is the sure possession of those alone who have the courage to defend it."
- Pericles
"The Nation that makes a great distinction between its scholars and its warriors will have its thinking done by cowards and its fighting done by fools."
- Thucydides
"Though defensive violence will always be 'a sad necessity' in the eyes of men of principle, it would be still more unfortunate if wrongdoers should dominate just men."
- St. Augustine
"From his weapons on the open road
no man should step one pace away;
you don't know for certain when you're out on the road
when you might have need of your spear
- Havamal (a viking age collection of common sense)
Gun Show Loophole
The concept of a gun show loophole is a work of rhetorical fiction. If a licensed dealer performs a sale at a gun show, they are required by the Brady Bill to perform a Background check. Further, they aren't authorized to sell handguns to individuals that reside outside of the state their license allows them to do business in.
All those other sales are simply private transactions between individuals. There isn't Federal legislative, regulatory, or Constitutional authority to interfere in these dealings. Some control has been inserted at the state level, in the Constitutionally unfriendly states like California and Illinois. Short of a firm registry of every gun to an owner, these laws aren't enforceable. Herein lies the strongest dilemma; every historic incident of a registry of arms has led to confiscation.
Mental Illness
Federal laws exist already to prevent those proven to be mentally ill, and found mentally incompetent, from gaining direct access to firearms. The complication is that several states aren't feeding into the NCIS database, following significant HIPAA concerns. Additionally, it takes a significant amount of work to properly find individuals mentally incompetent.
NRA
The NRA does not represent the firearms industry; this is an example of rhetorical misdirection. Their interests are parallels, but at its heart the NRA is a lobbying arm for the populace of these United States. Their sizable rosters and ability to mobilize individuals that have a personal investment in maintaining the rights protected by the Second Amendment, remind political representatives of their oaths to support and defend the Constitution. The members of the NRA care more about protecting their rights than the members of the anti-gun movement care to attack them.
Existing Biases
Each side is firmly entrenched in a controversial issue that has become increasingly controversial. Those supporting the right to keep and bear arms are exceedingly skeptical of any movement or issue raised by their opposition, citing historical examples. The strongest opposition lobby, seen as an enemy to those rights, is the Brady Campaign; they've built a strong, and consistent message focusing on minimizing gun violence and gun deaths, so "people really care."
The Brady Campaign characterizes gun violence as a "disease on our nation, where guns and bullets are the pathogens." Through careful messaging, they build the narrative to evoke strong emotional responses. Mistakenly, they've baked in outdated statistics, such as the 40% depiction of sales are private, though they paint all of those sales as dirty and with criminal intent. The emotional strikes are further weighted with tragic personal stories, adding weight to their lose adherence to facts. The milestones they set for addressing the gun violence problem are: Universal Background Checks, policing gun dealers, and adding Technology to firearms. Each of these creates a fundamental rejection from the proponents of personal firearms.
A system of Universal Background Checks, especially as implemented in California and Washington, places an undue financial burden on individuals seeking to sell their private property. Additionally, the law is entirely unenforceable in the majority of states, excluding California. That is because, unless a firearm can be connected to the individual that purchased it, there isn't a method to enforce the background check requirement. It would take an national firearm registration in order to enforce the requirement, a mechanism that is specifically banned by the Firearm Owners Protection Act. The reason: historically, registration of firearms has preceded confiscation (Germany, Australia, UK).
Federal Firearm Licensees are substantially regulated. There is a specific Government Agency responsible for such, Bureau of Alcohol, Tobacco, Firearms, and Explosives. Is it perfect? No. There are proven stores that have done illegal things, though the same could be said for every sector of the economy. The delay in strengthening the enforcement can be sourced back to an inherent distrust of the Government, backed by proven exercises of the Government exceeding its authority. Recently, the Firearms Industry's ability to operate as a business was threatened by Operation Choke Point, that caused banks to force the closing of business accounts for Firearms Dealers.
Then there is the push for Smart Guns, systems that use either biometrics or RFIDs to limit the actuation of the firearm to one person. The fast majority opposes complicating the firearm with an electronic system capable of interrupting the operation of the firearm. It is being pushed as a system that will prevent an unauthorized person from using the firearm; the responding fear is that the firearm will fail when it is needed to protect your life.