do you dispute the claim? why else would people ever "choose it" if they got ostrisized for it? in some countries they are executed. nobody would ever choose that or be forced to hide it otherwise. i've known kids (whether in high school or college) that were pretty clearly gay but never officially came out of the closet. why would you "choose" that only to hide it? it makes no sense. it's also not consistent with animals being gay. i doubt some penguins choose to be gay or can even make that decision.
not as far as they know. if it were purely genetic, it would have been an extinct trait, since gays are much less likely to reproduce, and thus pass down the supposed gay gene. the fact that we still have sexuality after centuries of oppression is a pretty telling sign that its not simply hereditary.
this isn't really relevant. its not like lesbian girls "wish they were guys" or gay guys "wish they were girls." they're fine with their sex, just have opposing sexual preferences. some people choose to have sex change procedures, but this is different than merely being gay