Free association means allowing gay people to lead gay lifestyles, but it also means allowing others to disassociate with them.
One of the very, very high points in the history of the gay community, from the libertarian point of view, was their fight against the police in New York City in 1969. This was the Stonewall riots, and the homosexuals and their supporters were entirely in the right.
Up until that time, the police would raid bars, pubs, bathhouses, etc., frequented by homosexuals. They would do so with impunity, with little opposition from gay men or from anyone else for that matter. But upon this occasion, they were met with fierce resistance and the relationship between these two groups of young men was never again the same. (Yes, apart from sexual preferences, there was not that much difference between the two; both were young men, for example).
Why did the police continually raid establishments patronized by this group of people? That was because it was illegal for consenting adults of the same gender to have sexual relationships with one another. These places were used by members of this community to meet each other for, among other purposes, such illegal relationships. This sounds horribly out of date to the modern ear, but in some Muslim and African countries such behavior is still illegal, and often severely punished.
The libertarian perspective is clear as a bell on this issue. No consensual adult behavior, whatsoever, should be banned by law. The gays at Stonewall were entirely within their rights, and the police, the law to the contrary notwithstanding, entirely in the wrong. (The Nuremberg trials established the justification of ex post facto law; just because an enactment was on the books does not necessarily render it justified.).
One might think, then, that homosexuals, at least a large percentage of them, would be libertarians. They were then, in 1969, or at least they were acting in a manner compatible with this philosophy. Alas, if it were ever the case, it is far from being true nowadays.
From defending their rights to freely associate with one another for mutually agreeable purposes, they have in the modern era moved to violate the rights of other people.
For example, many gay people now insist that others have a legal obligation to not only refrain from violating their rights by preventing their associations, but to actively cooperate with them in promoting their lifestyles. Thus, they are now willing to coerce bakers, florists, and photographers to cooperate with them in promoting their marriages with each other. Gays have filed lawsuits in court the purpose of which was to force others (mostly devout Christians) to violate their own principles.
Are these gay people acting in a manner compatible with libertarianism in doing so? Of course not. They are in effect asking the government to use violence of the sort previously employed against them at Stonewall, and for many decades before that time, against their present victims. They were in the right then in objecting to the treatment meted out to them, but are now in the wrong in instigating similar rights violations against those who now refuse to cooperate with them. Homosexuals have every right to engage in their consensual adult behavior, but no right at all to compel others, who object to these practices of theirs, to cooperate with them. Free association is a two-way street. Yes, gays should be allowed to enjoy the benefits of free association, but they should be prevented from denying those self-same rights to these Christians.
Are homosexuals wise to engage in such anti-libertarian behavior? It is difficult to see how they are. They comprise only something of the order of less than 10% of the overall population. Those who bitterly oppose their behavior still have significant numbers.
It is one thing for a powerful majority to pick on and violate the rights of a small weak minority. All too often, they can get away with it, unfortunately. It is quite another for a small group, despised by many, to stick their finger in the eye of people who greatly outnumber them. Are the gays overdosing on the movie The Mouse That Roared? This is a film where the great Peter Sellers played pretty much all of the roles. In the film, a small fictional country (think Monaco or Liechtenstein) conquered the mighty United States army in the aftermath of World War II.
This sort of thing can indeed occur in reality. David, after all, sometimes conquers Goliath. But in the long run this is the exception that proves the rule. Gays, if they were to consult their own long-run interests, let alone the justice of the matter, would forthwith cease and desist from getting the government to violate the rights of people far more numerous than they. A massive number of folks despise gay behavior in the first place, and this continual bullying of them will not likely induce any positive change in their assessments.
These victims of the present gay community are only human, too. They will grow to resent this mistreatment. Homosexual acts of this more modern sort are all too likely to boomerang against them. They would be well advised to limit themselves to their earlier, heroic, 1969 libertarian behavior.
P.S. I just saw the movie The Imitation Game, featuring Alan Turing and his machine (an early computer). He likely did more for Britain during World War II than anyone else, including Winston Churchill and all the generals and admirals put together. Yet, how the United Kingdom government treated this gay man, and many others in this category as well, was worse than despicable.