In my own personal opinion, I don't find it a choice 99% of the time. There are those out there who are either identify bisexual or just like *** or experimentation that can argue (the latter) that its choice strictly.
We are all either bisexual, and according to psychology, habitat, culture, beliefs, etc this influences whether we identify with a more male or female role. This would make sense because from the time we are born for the last 3-5000 years we have socially established gender roles that can and do directly influence our lives on a daily basis and certainly influence whether we identify with a male or female role...but that doesn't mean that a female can't identify with a male role or vice versa. However if we were all originally bisexual and throughout our lives either by choice or influence "decided" to be gay or straight, one cannot argue the fact that we still originally started out bisexual and being heterosexual wouldn't be "the best" way to be sexually. This could explain how one can go from straight to gay or vice versa (though the latter again is much rarer and usually only due to a strong willed behavioral change, or fear)
Now, the question stills remains when did you "choose" your sexuality? None of us seem to remember choosing, but plenty have opinions on the matter. Why is it assumed that if straight people didn't choose, gay people didn't either? It just doesn't make sense in my mind at least...its not logical. People do seem to be born the way they were born, and I don't hear of too many gay people choosing to be gay, just forced to be straight or asexual. When did our culture change to not except just love? (For those who don't know, it mainly changed when the modern religions came into play...Christianity, Islam, and Judaism)
Now i was born and raised a Chrisitian, and still associate with these beliefs...but on more spiritual level. I was raised to judge people who were different from me and be weary of anyone who didn't practice Christianity as i was taught to do. I never understood and was even hurt by the idea that God would be mean enough to only except those who knew him and Jesus, but not others who never had the chance? That doesn't sound like the kind all loving omnipotent God i know and when i started studying other religions...those didn't sound like God they knew God either (all 3 religions believe in the one mighty God). I know i just got off on a religious rant, but basically what i was trying to get at was that God made all of us in his image...Gay Straight Christian Islam Jewish Buddhist black white purple handicap not handicap blah blah and he made everything. Why do we bash God's creations?? God didn't put us here to do this shit with each other