As I think has already been mentioned several times in this thread...
Speaking here as an ex-gay and present bisexual myself, who has shared a lot of experiences with like-minded friends...
Both 'choice' and 'genetics' are very loose terms that serve only to conufse. 'Choice' implies you just suddenly decide at some point "I will be gay now," and maybe the next year think "now I shall try being straight for a while."
"Genetic" implies that it is something you directly inherit or is a result of some abnormal function in your genes. Omega has already ridiculed the idea of a simple 'gay gene', but te extent to which this is misleading goes beyind that simple misunderstanding.
And whilst we are here, talk of 'upbringing' brings in the odd idea that upbringing means if you are brought up near gay people it makes you more likely to be gay, or if you are not, that proves it is not upbringing. As a double comment on that scientific piece above, first of all to say that gays etc. grow up in a straight world is to miss the sexual subtexts that everyone is bombarded by from school age upwards; secondly, and more the point of what I am saying, upbringing is about the events in your life making you more open, more receptive, more accepting, or more rejecting of various factors of your being, NOT that you see x and so y happens.
Your sexual orientation is part of your personality. People are many, many things in life. Patient, impatient, angry, calm, sour, depressive, self-loathing, self-loving, obnoxious, shy, brash, arrogant, quiet, boring... now, how do these things come about? You don't just choose them. You aren't just born with them. it's not just down to what has happened to you in your life.
Let's face it, it is all of them. Your personal decisions are a major factor in who you are- "A man is the sum of his memories," and "We cannot choose who we are- yet whar are we, save the sum of our choices?" are two quotes that neatly sum this up. This is NOT saying "I will be this or that," this is that the way you react to events, reflectively observe events after they happen, consider the implications of those events, and then act differently in future, are all factors under your control- even if not totally consciously- that go towards making who you are.
Your upbringing decides the source material for all this information, and the people for whom you will chose as role-models to help base those choices upon. So again, this is a vital factor.
And yes, everyone is born with certain genetic predisposiitions to certain things. Note predispositions, NOT certainties, and that this is only one piece in the larger puzzle that is someone's life.
And this ABSOLUTELY applies to sexual orientation as much as it does for everything else. It is a long combination of life factors that influence who you are sexually attracted to. It is NOT a set certainty for some, for others, it is rigid. The underlying reasons behind this- personal choice, upbringing, and genetics- are exceedingly complex and should not be simplified.
And so, in as such that it does not harm anyone- well, not more so than other lifestyles- there is no room in the modern world for treating this lifestyle choice differently. But one myth should be shot down- that all gays get pissy if you make out it is a choice, not preset. Some gays get JUST as pissy if you say it is genetic, because that implies- and is often said this way- as if it is not their fault, pity what they are born with, because they cannot help it. Many Gays don't want to be accepted because people think they cannot help it, they want to be accepted because it is RIGHT, and because it is valid. Accepting it on the idea they have no choice is not really equality at all. So it is absolutely vital to recognise this element in someone's make-up, and not to confuse this view with the view of some Church's that therefore 're-orientation' is a good idea, as if it is ever healthy to force personality change like that even if it WAS right to make people straight, which it is not.
And so every time you hear someone say "Let them be, they can't help it..." consider to yourself- is it not the subtext of that comment that if they COULD help it, they should? If you turn around and ask these people "So what would you say if they COULD help it..." you may reveal a more sinister mindset than at first seemed; treating homosexuality as an unfortunate thing to be pitied, rather than the valid choice people want it to be. Ok, it's not as bad as gay bashing, but the statement itself is still evidence of inequality. Whether they can help it or not shouldn't even be an issue.
So please bear that all in mind...