@jaken7: Greeks and Romans especially. Nature tends to find a way, in the end, to keep things under control one way or the other, the same argument can be made for some of humanities largest illnesses and even natural disasters that keep humanity and all living organisms in check. Religious people would see this as god's influence but from the non-religious viewpoint everything on this planet is part of one large symbiotic system, everything is connected one way or another and while people tend to ignore it overpopulation is a huge problem for future sustainability.
Has anyone ever thought that maybe just maybe homosexuality is a naturally occurring phenomena brought on by overpopulation? The increasing amount of homosexuals through the years has never been a proportional increase but it does seem to inflate naturally when society/humanity reaches a point of overpopulation and excess (greed/wealth/power) (and it also seems to occur when religion is at it weakest i.e. less control over the masses). While procreation may be hard-wired in us as a natural imperative to further the species it would also make sense that something would be present to insure that said species would not grow to the extent that the environment would no longer be able to sustain it, if you look at animal species they rarely overpopulate naturally, it is only when other factors (new environs, humans, unnatural changes in the food chain/weather) are brought in that causes their overpopulation. As it is humanity is the one species that has been advanced enough to ignore a lot of these natural instincts and the Earth is paying the price, in the future homosexuality could be the thing that keeps us from destroying the planet cause humans sure as hell won't ever allow any man made laws decide how many kids they can have.
Also the view of procreation being a valid argument against homosexuality doesn't hold up against evolution and nature, humanity could never die out just from homosexuality, even if the entire human race was gay we wouldn't give up, even ignoring science and what can be done medically to conceive a child you don't have to like having sex with the opposite sex to procreate, men and women have probably been having sex with the opposite sex even when it repulses them since we lived in caves.