I haven't read the enitre thread, so forgive me if this has been said.
Think of it this way: If you're straight (chances are that you are), did you ever make a conscious decision to be attracted to the opposite sex? Assuming you didn't, what makes you think gay people made a conscious decision to be attracted to the same sex?
If you believe they did make that choice, why did they make it? Homosexuals are undeniably subjected to huge levels of abuse and discrimination. If they made a conscious decision to be gay, surely there must be some advantage that homosexuality holds over heterosexuality that would negate the life of persecution that inevitably follows a choice to be homosexual? As far as I'm aware, sexual relations are no more or less satisfying for gay people; long term relationships are similarly no more or less satisfying; it's certainly no easier to start a family; career prospects are not improved by being gay; there's no significant difference between gay people and straight people when it comes to quality and number of friendships.
From what I can see, there is no inherent advantage to being gay, yet there is at least one huge disadvantage; that of a life of abuse and persecution- it cannot be denied that gay people experience more prejudice and abuse than straight people.
All of this leads me to one simple question; if you had a choice, completely free of any physiological influence, why would you choose a life frought with abuse and persecution?
If anyone can think of a reason, I'd be delighted to hear it, but the only conclusion I can draw is that homosexuality cannot be a conscious choice. That isn't to say that someone's sexuality cannot be affected by environmental factors, but I do believe that there is a physiological predisposition to homosexuality (IIRC, there have been studies that have shown that sexuality can be affected by pre-natal hormone levels). Again, assuming that there are environmental factors (nothing is ever wholly nature or nurture, after all), I have no idea what they are, nor would I care to speculate.