And sometimes you can just tell really early. There were a couple of kids in my high school that I just knew were gay. I could tell from mannerisms -- things like voice tone and mannerisms are substantially genetic. I thought to myself, these guys are gay. And it wasn't anything environmental that did it to them. They probably knew from a very young age that they were gay, just like I knew from a young age that I was straight. I knew I liked looking at the lingerie-clad models in the JC Penney catalog, haha.
Now that doesn't mean that people need to support gay marriage simply because it's most likely an inherited trait, like eye color or handedness. Quite the contrary. But I am completely unconvinced that it is a choice. I don't see the benefits that homosexuals are getting by choosing it. What benefits does society confer on them? Why would someone choose to be gay today?
Nope. I haven't seen any evidence to make me believe that someone chooses to be gay. People can debate the ramifications of homosexuality all day, but I think that people are largely born gay.
BUT, for a growing segment I do think it is a choice or more a pathology. Especially as society becomes more ill.
People choose all sorts of self destructive behavior for complicated reasons.
Irving Bieber, before the homosexuals mugged the American Psychiatric Association and took over all the committees on the subject and began enforcing PC, did a longitudinal study of homosexual men in the late 1950's and early 1960's.
He looked at whether psychotherapy could help men who displayed homosexual behavior, which in turn involved some inquiry into the etiology of homosexuality.
Long book cut short, he concluded that about 1/3rd of homosexual men are "hard-wired" (i.e. "essential" homosexuals), while other groups display varying responses to attempts at psychotherapy and conversion therapy. He was attacked by the gay cabal, who tried to discredit him and terminate studies like his.
Nevertheless, in the 1990's, some 35-40% of healthcare professionals still believed, like Bieber and against the best propaganda efforts of the cabal, that homosexuality is primarily psychological (and therefore susceptible of psychotherapeutic amelioration).
The "essentialist" position is basically a lawyer's position, and not science; it's an argument the gay lawyer corps wants to push on the Supreme Court, that homosexuality is an "is", i.e. an essence (like black skin), and not a behavior or choice (and therefore subject to society's legislation and undeserving of the Supreme Court's highest standards of legal protection).
Interestingly, there are a significant proportion of gays who believe that sexual identity is "constructed", plastic, fluid, and changeable. Which means they are not on the same page as Lambda Legal, which will have somehow to keep them out of the courtroom.