Here, one can see a bill "To end membership of the United States in the United Nations."
What do the proponents and opponents of the bill state to be advantages and disadvantages of approval of the bill for the US?
Representative Rodgers, who introduced the bill, put out a press release explaining why he did it. More generally, various people have called for less involvement with, or active rejection of, the UN; for instance, WND.com carries a call for a petition that reads in part,
The United Nations has voted more times to condemn Israel, the shining light of democracy in the Middle East, than North Korea, the rogue communist regime. Or Somalia. Or Vietnam. In fact, more than all the other nations of the world combined.
It also adopts procedures and policies to override national law and advocate for abortion.
It routinely appoints nations with questionable records on human rights, such as Angola and Senegal, to its Security Council.
It threatens Americans’ constitutional rights through its Arms Trade Treaty and even parental rights through its Convention on the Rights of the Child.
But its latest condemnation of Israel, with the full acquiescence of the Barack Obama administration, is one step too far, charges a new petition that urges the U.S. Congress and incoming President Donald Trump to do something about the international institution.
Such as defund it.
And discount its decisions and pronouncements.
And deport it.
In other words, proponents of such a bill presumably believe that defunding the UN would protect American sovereignty and morally cleanse them from indirectly supporting repressive governments; but the last straw was Resolution 2334, which is widely perceived as hostile to Israel.
I expect that there are a lot of arguments, some mutually contradictory, that different opponents would use against the bill. Some people (including some U.S. Citizens) might say that the U.S. ought to conform to the full corpus of modern international law, that it has a moral imperative to support the development of less-privileged societies, and that the U.N. resolution on Israel and Palestine is valid because Israel is a tool of white oppression.
Others might agree that some activities of the U.N. are troubling or ineffective, but also believe that overall the organization and the framework in which it operates does a lot of good; more of a "don't throw the baby out with the bathwater" argument.
There is a MoveOn petition against the bill; as of this writing it has only been signed by three people and the body is short enough that I can quote it verbatim,
This bill is a pre-cursor to Ending the United Nations! This puts not only our country and family at stake but may end the planet.
Either way, an article in The New American points out that similar bills have been introduced in previous congresses:
By introducing the bill in this session, the congressman from Alabama continues the long and valiant effort by lawmakers to get the U.S. government out of the UN. Former Rep. Ron Paul (R-Texas), a GOP presidential candidate last election and a hero of many liberty-minded and constitutionalist Americans, first introduced the bill in 1997, when it garnered 54 supporters. The next time it was voted on, support had drastically increased.
One of the largest arguments against the US leaving the UN is because of its status as one of the 5 permanent members of the UN Security Council. Should the US leave, it would lose veto power for proposals introduced by Russia and China, and as such would have to curry favour with France or Britain to veto the proposal.
This hurts American interests as it's unlikely that either Britain or France would change their minds about supporting a proposal unless the US gives them something in return.
Another argument against it would become blindingly obvious if you ever visit the UN and talk to one of the tour guides. Hundreds of thousands of meetings take place each year in the various UN buildings. They're one of the greatest tools of International diplomacy ever conceived. Should the US leave, it would have no standing or say in the meetings that take place, only allowed to offer an opinion that the rest of the UN are completely free to disregard entirely.