"You should be able to choose your attraction to men. I dare you to try it, right now, for one hour. Will yourself to be physically aroused by men for one hour. If sexuality is so malleable, you should be able to will yourself straight again, no problem."
I can do that
According to certain fields of psychology just about everything in the human psyche is malleable, but that's mostly coming from people like John Lily and Timothy Leary. So take it for what you will.
However, something I always found interesting on the subject was their "Reimprinting" ideas. Apparantly they opened a clinic that did stuff like this(it's essentially akin to certain forms of brain washing, i guess) and had a customer who, upon the first time he was having sex, had a police officer knock on the window of his car and scared the shit out of him so he was impotent for umpteen years.
The theory behind that is socio-sexual complexes are generally imprinted on the first sexual experience, but I'm sure they include prior life experience to some degree.
Anyway, once they opened the clinic he came and they apparantly helped, and he was able to get it up again. I'm sure there's a more detailed report out there somewhere.
This guy makes me laugh everytime i think about him, though, he's such a whiner.