There was no choice involved, and that's the point.
Neither one of (I assume) had to sit one day and ask ourselves "am I sexually attracted to people of the opposite sex, or am I sexually attracted to people of the opposite sex?"
I did not, and I am assuming that neither did you.
If homosexuality is a choice, then I could choose to be attracted to men...I can't.
If I can't make the choice, then I must not have a choice, and if I don't have the choice of finding men attractive, then the whole "homosexuality is a choice" theory is crap.