I guess I missed the memo but it seems that it's now verboten to suggest that humans have any sort of choice at all in terms of the gender of the person(s) with whom they like to have sex. I say this because apparently Cynthia Nixon got into hot water for saying that she had chosen to take up an intimate relationship with a woman. (link). I think I understand the reasoning for it -- some might worry that the notion that gender preference might not be strictly biological will invite suggestions that "pray the gay away" therapy might work and/or that instead of society making room for gay people we can instead just get homosexuals to choose a different orientation. Also, if it's strictly biological, the story seems to go, it's more obviously unfair to deny them the rights and means to live the same sort of life that straight people have.
I think the obvious problem here, that both sides seem happy to ignore, is that almost all preferences we have involve a complicated mixture of biological and environmental factors. I recall learning or reading that sexual preference may well be more of a spectrum than a simple on/off switch, i.e., while some people may be heavily inclined to be straight or gay, there are lots of people in between that might be more or less interested in having sex with person of the same or different genders. But this is obvious, isn't it? Don't lots of people who eventually settle into a gay or straight lifestyle experiment in their youth w/ differing preferences? Are we saying that all those people were simply violating their biological destiny? We believe, I assume, that there's a strong biological component that influences other features that we find attractive, but we wouldn't be surprised to learn that a person who had previously preferred buxom blondes or tall women was now choosing to spend more time with short slender brunettes.
That aside, I also think it's worth thinking about why the extent to which homosexuality is fully biologically determined matters so much with respect to the civil rights issues. Consider that there's probably a strong biological component in whatever the makeup is of a person who becomes a psychopathic killer. But if we were to firmly establish that that were the case, it wouldn't follow that society had some sort of duty to accommodate them in this compulsion. OTOH, many of our civil rights have no biological basis. We believe that people should be free to say what they want, believe what they want, and worship as they wish. The basis for this isn't the belief that beliefs and utterances and religious practice are all biologically determined. I think the civil rights story is a pretty simple one. We don't have the right to do whatever our biology compels or inclines us to do, we base civil rights on considerations of the fact that there's much inherent utility in maximizing liberty especially on matters that have little or no effect on the rest of society. Why does the fight for gay rights have to be depend on any more, or something other, than that? It's ironic that the civil rights movement which spent so many years arguing, implicitly or explicitly, that biology is not destiny, now finds itself vehemently insisting that is.