I read a question asking if communism was inherently authoritarian as it is often portrayed. President Nixon often talked about countries being either communist or free. Is democracy always the opposite of authoritarianism?
If we imagine a pure democracy where the government faithfully executes the decisions enacted by a majority of the people, its level of authoritarianism would necessarily be decided by the people. In theory, people could vote that the government should perform routine searches of houses for contraband without prior cause, or arrest and imprison people without a right to habeas corpus or to retain counsel on their behalf. Pure democracy as a concept has been criticized for allowing a "Tyranny of the Majority", the idea being that if a group holds majority voting power they can make decisions that are to their benefit over the minority voting group in the country, as opposed to making decisions that they believe will benefit the country as a whole the most.
Western-style liberal democracies obviously do not work like this, they have some set of rights, documented explicitly or otherwise, that the government cannot routinely curtail without either a supermajority vote or some kind of judicial oversight or procedural restriction. There are also generally legislative controls to prevent the "Tyranny of the Majority," such as veto power for the chief executive of the country on bills or legislative procedure that allows de-facto vetoes by minority voting groups (such as filibuster in the US or quorum requirements). This is probably the kind of democracy Nixon was referring to, and in opposition to Soviet and Maoist-style communism as opposed to idyllic Marxist communism, which would probably have some kind of democratic or republican component for the workers to make decisions about the country's public policy and could even have a constitution laying out fundamental rights that the proletariat are entitled to that the government actually adhered to.
Ultimately though, any form of government can be authoritarian. The US certainly has a sordid history of authoritarianism, such as eugenics laws in the early 20th century, warrantless internment of Japanese citizens during World War 2, and the way that it has used the current "War on Drugs" and later the specter of terrorism to vastly expand its police and surveillance powers. In theory a democracy is more receptive to the will of the citizens, but politicians and institutional media are experts at getting the public to agree with measures they want to put through. Despite all this, it's still accurate to say that liberal democracies tend to be much less authoritarian than dictatorships.
Defining Democracy and Authoritarianism
For this we should consider Democracy to be defined as a government where citizens elect officials to represent their interests (representative democracy, which is what most people think of when they think of democracy) and Authoritarianism to be a concentration of power in the government such that any public dissent from the status quo as set by the state is met with swift and brutal repression. The "status quo" includes whichever person or party is currently in power, and thus alternative political parties are generally not allowed to compete - either by law or by jailing political opponents. Authoritarian governments generally have an Autocrat for reasons that are probably out of scope for this question, but this is not necessarily the case.
Is Democracy inherently anti-Authoritarian?
Arguably the most important aspect of Democracy is a peaceful transition of power when people vote against the current ruling party or person. This is inherently anti-Authoritarian in that an Authoritarian government or Autocrat would not accept this transition of power, and would respond with force.
However, there is an old phrase "Democracy is two wolves and a lamb voting on what's for lunch". Just because a majority of people (or however the given Democracy apportions voting power to its people) support something doesn't make it non-Authoritarian. If a majority of people support giving the government the power to grant minorities less rights or to execute drug traffickers this is certainly an Authoritarian stance, but it is not anti-Democratic.
It is also possible that a country which is ostensibly a Democracy can become an Autocracy with popular - if temporary - support from the people, such as how Maduro went from President to Autocrat. That said, Democracies generally create a separation of powers with checks and balances to prevent a ruler from seizing absolute power.
If you are looking to contrast Democracy with another type of government in this vein, it should be Autocracy. There are aspects of Democracy that are anti-Authoritarian, but being a Democracy does not mean a country is not Authoritarian, it just means that a majority of those given the power to vote support those Authoritarian measures.
In principle, yes. In practice, no, for it depends on the specific implementation of the democratic process in the structure of the government. For example, Venezuela is democratic in form (there are elections and an opposition), but authoritarian in nature (results of election are ignored or changed, opposition are persecuted, coerced, etc.). Even in the US, if the president exerts control over his party, which in turn is the majority in the Senate and House, then the president may govern in an authoritarian manner...
"Is democracy always the opposite of authoritarianism?"
Yes, the democratic system and authoritarian are two poles that stand against each other. They are mutually exclusive.
In an authoritarian state, only a single person, with or without a group of chosen elites (party), dominate the state's social-political agenda. In such state, the opposite voices/views are suppressed through political persecution, regardless of whether the voices/views are supported by the majority or minority.
On the contrary, a democratic state respects the voices/views of the majority, regardless of the correctness of the majority voices/views, but, unlike the authoritarian state, the opposite voices/views are allowed to be raised/heard/expressed freely without the worry of been politically persecuted, and the minority is permitted to work from within, and have the chance to prevail ultimately.
Both democratic belief and authoritarianism can form a good/bad government. The direction of the former depends on the opinion of the majority that may swing/alter from time to time; the latter depends solely on the opinion of a single person that usually lasts with him/her regardless of other opinions. Clearly, rule by a single opinion is on the other end of rule by the opinion of the majority.
A government is a legal (as opposed to moral) monopoly on force. The government can compel you to do what they want, backing up the instruction with brute physical force. Fines, jail, up to execution. Any form of government can produce tyranny, since power is placed under government control.
A government system may work if authority and responsibility are not too unbalanced. If a government leader can do whatever he feels like and not get punished, he (or his successor) will soon find he really wants to do stuff to stay in power. Just about anything to stay in power.
The idea of democracy is that if somebody gets out of line he gets out of office. For this to work requires several things.
The institutions surrounding the process must be sound, not corrupt. The police (of all levels and whatever form) must stand apart from the process and enforce the rules. The rules must be good rules. The courts (or whatever the equivalent mechanism for deciding such things) must be non-corrupt. The election process must be pretty close to perfect, allowing as little corruption as possible.
The news media must be non-corrupt, at least most of the time and on balance. It can work to have confrontational news media. Leftist press and rightist press balancing out, for example. But it is less than ideal.
There must be mechanisms for information to get out about how bad a given government is so that the voters can see who to vote for. Or more importantly, against. So things equivalent to free speech are critical. In a country where the government decides who can say what, tyranny is never far away no matter the political system.
People must be educated. If the government runs the schools there is a huge instability. It is all too often an irresistible temptation for a would-be tyrant to enact "just a little" education reform. And before you know it, 17% of university profs are communist.
But education is required. People have to understand the nature of government and how quickly it can become horrible. No matter how much you like the current leader. No matter how perfect and moral you think he is. He won't be there forever. So, if you give him new power, even if he does something good with it, that power is now attached to the office. And the guy who comes after the current leader may not be nearly as nice.
So, democracy is not inherently anti-authoritarian. If you add voting to a situation with corrupt institutions, a corrupt news media, and a non-educated populace, you won't get freedom. Even if you have, for the moment, a good leader, it will last at most the life of that leader. And it could easily tempt that leader to turn.