I don't think anyone really knows what causes people to be gay or not. I think that when you look at the statistics you do see a definite trend towards gay people being more likely to have been sexually assaulted. Whether that is because they are gay to begin with or whether that is a contributing factor to the development of their sexuality I think is still up for debate.

The problem with the religious right, and well the religious left as well, is they want really simplistic descriptive explanations of life. For the right they want some nurture explanation since it removes the need to reconcile the idea that god might have made someone "imperfect" with the reality that gay people exist. That leads to situations where they can insist someone has been abused or something is wrong with them when no such abuse or problem exists. I've experienced similar responses when approaching religious types with questions about how to deal with depression. Their responses essentially came down to, "you've not prayed about it enough" which isn't a particularly helpful response, since it assumes that you first hadn't prayed about it, and second that it's something that you did which is wrong. When neither may be the case. Responses like this were very instrumental in me developing my own opinion that most religious people use god as a form of double think, a cognitive dissonance that allows them to maintain prescriptive moral judgements on others they wish to propagate while completely removing themselves from having to think about the failures of such ideals.

The left side of things takes a similar prescriptive approach though theirs follows a more thoughtless acceptance of everyone and anyone without any kind of underlying critical thought about what the end result will be.

I think with this issue specifically we kind of get caught between the elephant in the room of gay people being sexually abused at inordinately high rates which can't be discussed without straying into the overly gay bashing types that want to persecute people who basically just want to live with their partner of choice.

So really the question of is it a choice or not vs rather you are born that way or not really just comes down to an answer of "it's both" and everyone is a bit different. But we can't actually talk about that in public since you'll manage to piss off most everyone on both sides of the issue with such an answer, so most people will choose one of the socially acceptable opinions to hold.