It looks to me much like an affliction than a choice. I'd be able to vote for a homosexual (heck, I think I did, more than once, in South Carolina) if there was an understanding that he/she should be about representing the interests of constituents and not be about advancing an agenda about sexuality.
I believe it can be both. I have not studied this closely by any means, but an educated guess would be that 1-2% of the population may have a biological component that would give them the "affliction". The rest are primarily young people(or began as) sucked into a perverse behavior by abuse and by a culture that says anything goes, and who are you to judge the "officially state accepted"(PC) behavior of anyone?
Either way, the vast majority of these people have extremely compromised moral principles, or none at all. They see a moral, ordered, healthy society as a threat to their primary personal identification and source of sexual gratification.