I think the evidence is quite clear that homosexuality is far more complex than a simple genetic disorder. I compare it to alcoholism, in that alcoholism arises from at least three factors; a genetic predisposition to become addicted to the chemical, a culture that supports abusive drinking; and choice to drink too much.
Similarly, I believe that homosexuality arises from those three factors: a genetic predisposition, a culture that accepts and promotes homosex and encourages those behaviors, and choice.
For 30 years I've known a couple that has 4 sons: 3 straight, 1 gay. I also know that the gay son had a big crush on an GIRL when he was about 12. If homosexuality were purely genetic, people wouldn't want a girl at 12 and a guy at 25.