I agree with almost everything you say but your first point about it not being a choice, i dont think its as straight cut as that i think it can be a choice as well.
so whn did you choose to be straight?
Evolution is the adaption of a living thing over time to it's environment and conditions so it can survive and continue the cycle of life, having a gay gene would totally go against that. If 99% of the world population had the "gay gene", we would be in serious trouble wouldn't we? How would you pass on a "gay gene" anyway?
if you wish very very hard nitefly mgiht pop up and explain the science behind it.