Whenever I read of a study of gay vs non-gay physiology – and there have been several – there is usually compelling evidence (if not outright proof) which indicates that the vast majority of gay people are born that way. Specific areas of the gay brain are sized and “wired” like the opposite gender’s, not like the straight version of their own gender.
In my mind it’s sort of like evolution. Sure, it’s still just a theory, but if you don’t “believe” in it, you’re most likely an idiot (or choosing to remain ignorant, which is the same thing).