But the same hold true even if sexuality is NOT biologically determined, so your point is moot. Actually, even if some sexual deviance is indeed biological in origin, we can still prohibit it (pedophilia) when we judge it by the criteria of what rights are violated because of it (children should be protected from manipulation by adult predators
You haven't demonstrated this point philosophically as of yet. All of your prohibitions, including those regarding adult/child sex, are nothing, outside of an overarching value system not bounded by purely human
cultural dispositions, but a "yuck" factor imposed by the dominant groups in society upon such behavior. That we can prohibit such behavior no one is arguing. However, the entire Gay Rights movement's arguments, and those of the cultural Left in support of them, are arguments grounded in moral and cultural relativism. Neither side here, the Left or the Right, would take you seriously Asbestos, because you offer no guiding set of values except Machiavellian ones based upon majority rule and the majority's opinion of what is acceptable and what is not. Conservatives seek to preserve the best of traditional sexual norms. The Left seeks a complete redefinition. Simply throwing up one's hands and deciding to prohibit or not prohibit, outside of the body of value judgments upon which such decisions could be made, is pointless, and purely utilitarian (while the issue is fundamentally moral and, ultimately, metaphysical, grounded in ultimate values).
Some societal norms should not be enforced by rule of law. Religion is one of them. Let people choose whether to believe in God. Let people choose what sort of sexual lifestyle they want (so long as they only do so with consenting adults). Again, I'm not for homosexual marriage, but I think government should get out of marriage entirely and only concern itself with the rights of children and parents without making government give a special stamp of approval to certain adult relationships.
The problem here, Asbestos, is that the state, both legislatively and judicially, is already enmeshed up to its ears on the issue by ignoring the Constitution and imposing a massive defacto redefinition of the term "marriage" on society while vast majorities of Americans, liberal and conservative, have been clear in poll after poll that this is going too far.
In some things, we cannot simply "get the government out" of this or that. that's a nice sounding Libertarian sentiment, but in practical application can come up quite short. Simply allowing "Gay" marriage, by definition, redefines and reorients the entire concept...precisely what the homosexual movement desires.
Political pacifism can bring about, in many cases, the same outcomes as aggressive activism. All it requires, as Burke noted, is that the people such social changes will effect do nothing.
The state should, in its negative power to protect and guarantee the unalienable rights and liberties of its citizens, prohibit homosexual marriage, as homosexual "marriage" is ultimately incongruent with a functioning society based upon those principles.
The state needs to guarantee the definition of marriage just as it needs to guarantee the right to assembly or speech. The society, to continue as a self governing free society, depends upon them. Upon the meaning of words hinges the fate of a nation or people. Marriage is not a "right" in the sense of the others, but it is, as a cultural institution, pivotal to the continuation of a free, civil social order.