I did provide scientific evidence with the brain study. What you are looking for is a "gay gene". Which may very well not exist. Genes aren't the only determining factor when it comes to behavior. Perhaps you didn't see my post or simply ignored it.
The human brain is a vastly unknown entity. Mostly because the only way to study it is after a person has passed. Like in the case of Alzheimer's. Even in animals...the only way to confirm a case of rabies is to examine the brain of the destroyed animal...sure, an Alzheimer's patient displays symptoms of the disease, and a rabid animal displays symptoms of rabies...but the only way to confirm it is to actually look at the brain physically.
The bottom line is that homosexuals are a rather static group....there's no real danger of a heterosexual man or woman "turning gay". So the thoughts of our population being decimated by people who can't procreate is ridiculous and backward thinking. The religious angle only has merit if you believe that you are superior to.others and have the power of God to judge others despite your own human nature to sin....which, once again...is ridiculous and Backward thinking.
Personally...I don't give a shit. If gays want to get married, more power to them...I hope they get that right. Because one thing(and yes, I know it's judgmental) that I don't like about the homosexual community is the promiscuity that exists within it. I think that has to do with them being viewed as outcasts though, and if they are "mainstreamed" into our society, they will find equilibrium and have more "normal" relationships. I mean, sure....there will have their share of "sluts" who stay single and fuck everything that moves, and there will be those that think they want monogamy and get married only to cheat on their spouses.....but we have that in the heterosexual arena too.