If it wasn't a choice, or couldn't be a choice, I'd be completely sure we're all fucked up. It would take some advance in bioengineering to produce a completely artificial way to alter a person's sexuality. If such a thing could be possible then for me humanity would be dead, we would be nothing but merely a cumulous of electro-chemical reactions meaning that any moral code, any feeling, any idea is result of nothing but chemical reactions band so is modifiable by altering these chemical conditions.
I used to have the theory that we all are born bisexual and somewhen in our lives we take one of three possible options dependiing on what appeals most to us. Else I think that there are several factors from emotional to´physiological that given certain circumstances may influde in someone's sexuality.
There's for example people that have had completely straight lives for 40 years and they say that they've got ired of women and decide to have sex with men. Many ex-convicts develop either homosexuality or bisexuality.
Since now there is less rejection towards homosexuals many feel more confortable to explore homosexuality and become more akin to it given my theory. Also there's more exposure to homosexuality than ever before so more and more people become curious about it.
So I think homosexuality is the result of a combination of biological, physiological, psychological and social conditions.