I believe it is likely more nurture than nature but I also believe that people that say being gay is a choice are wrong, (not bad or evil, just wrong) because I have yet to hear any straight person (myself included) tell me when they made the conscious choice to be straight.
That's an important point many talk right over. I think if people slowed down long enough to discuss the issues, there would more light than heat generated and I also think many or most would agree with you.
Where the confusion stems, I believe, is that many mean the behaviour is a choice, not the same-sex-attraction and when they don't clarify their position they lose some of their audience.
Now, I have to clarify something myself. When I say same-sex-attraction isn't a choice, I mean that for most cases. The only reason I bring this up is because there is an adamant group who claim to have chosen their same-sex-attraction. I'm referring to the Queer by Choice group.
For the vast majority of those with same-sex-attraction, I believe the evidence supports it's not something they choose, but at the same time they are not born-that-way. It's not a topic that can be easily understood with only a cursory look at the evidence.
Current research suggests that the moment of choice is not always a conscious one. What straight guy is going to admit that he chose being straight; that would mean he’d have to admit he considered being a homo. WHo would admit that?
My own view is that it's a fetish, much like any other, and that it is very strong. I don't suppose that anybody makes single decision at any point in time to suddenly acquire some fetish (like... say... feet). But I don't think people are born with intact fetishes either. I think it's the result of a long process of both conscious and unconscious conditioning of the mind, over a lifetime.
It's not that people "choose" to favor boobs and some favor butts. Or that anyone "chooses" to be into bondage or whatever else turns them on. But over time, those things have developed and formed into a set of preferences. And fetishes do evolve over time, and can diminish in favor of something totally different.