Oh my, a religious debate. I'm not going to say whether I agree, disagree, or anything, but rather go back to the question I had before and give my personal stance on it. Feel free to disagree with anything I say - assuming you have reasoning to back it up.
First of all, I'd like to state that sexuality falls under the realm of psychology.
Second, for the people who haven't taken a psychology class, it falls under the realm of 'nature vs nurture', or 'biology vs environment'. In other words, is it predisposed from birth or caused by the external world after conception?
Third, my personal stance: It is a combination of the two - nature and nurture. There are studies of homosexuals (sadly, most are on males in my knowledge) which have said that the more children a woman has, the more likely the next one will be homosexual (as an example) - I haven't heard of stress possibly causing homosexuality, but I suppose it's possible. As for the environment, I think that's more of an obvious one - a culture which accepts homosexuality is more likely to have homosexuals, while a culture that is less accepting is less likely. Research has shown that this is could be more relevant than genetics in determining sexuality.
I'd say that if it is up to choice, that 'choice' is largely determined by the environment and culture, so it could be argued that it's not really a choice at all. To me, it's more like (I HATE to use this as an example, because homosexuality isn't a bad thing) the likeliness of alcoholism - choice plays a role, and can determine sexuality, but the likelihood of this choice is determined by genetics and the environment.
I don't exactly have firsthand experience of what it's like to be homosexual since I'm actually asexual, but I think that this makes sense. Thoughts?