I've never met a homoloveual who was born with homoloveual tendencies.
Why do you think someone would risk destroying their relationship with their parents, friends, and family to come out? Definitely not because they just "decided" to be gay. If you think that hormones and chemistry makes guys be attracted to chicks, why is it so insane to think that those same hormones and chemicals could make you hardwired for members of the same camp?