I don't know why he'd do that, nor do you, just like neither of us knows why a man or a woman develops an attachment to a certain paraphilia. No matter how fierce the attachment is, we don't frivolously and ignorantly invoke science to sanction it.
As far as I'm concerned, no, I don't imagine there's a force on earth that could make me do that. Others, however, proved otherwise, and I do them no injustice when I hold them accountable for their actions.
Acceptance of homosexuality in the U.S is a fresh affair; it'd be improper to use it as a gauge. Countries with a longer history and more established tradition of acceptance of homosexuality are the benchmark. In a recent YouGov poll, nearly half of British youth profess not to belong to either ends of the sexual spectrum, but to be somewhere in the middle. The percentage is much lower among older British generations.
(LINK)That is to say, longer exposure to a certain societal view/practice from an early age greatly biases human behavior. It's unfortunate that I have to explain this to those that proclaim themselves the blessed enlightened.
No one comes out "heterosexual"; we're so by nature. As such, why would I object to people for being that?