Homosexuality is just nature's last resort in trying to deal with our over-populated world. It has always existed. Gay people can be traced back to Ancient Greece (maybe even earlier). It's just become a lot more common lately as our population gets more and more out of hand.
There are plenty of studies out that have concluded that homosexuality exists in the animal world. And no matter what some religious people will say, humans are animals. I'm not saying we evolved from apes or anything (actually, I am saying that, I just don't want to get into that debate right now), just that we belong to the animal kingdom and we aren't some special super race all on our own.
Homosexuality, from everything I've read, seems to be nature's way of dealing with overpopulation. If you put two mice in a cage and let them reproduce over and over and over again without giving their family more space to grow, they will start to show signs of homosexuality and eventually stop reproducing altogether. This, along with lower fertility rates, is just nature's way of saying there are too many of them and it's time to cut back until some of them die off.
Humans can be compared effectively to that experiment.
We have the whole world at our disposal, and we have stretched its resources to the max. We live in huge cities, in huge apartment buildings, 60 storeys high, one right beside the other, like so many cases of sardines in a warehouse. We fight far harder for our survival than any other creature on earth, using our advanced medical sciences to defeat every epidemic that would naturally cull our numbers. We have extended our life spans past 100 years when we originally only lived to be 50 or 60.
By doing so, we have disrupted the natural balance that once existed in this world, and we have dug ourselves a deep hole that we will not be able to get out of unless our numbers suddenly go down, because there just aren't enough resources to go around.
Homosexuality is just nature's last resort in trying to deal with us all. Maybe, once we finally get past all the discrimination and can see that people are all just people, the human race will start to thin out. Our numbers will stabilize, there'll be enough resources on earth for everyone to survive off of, and we'll go back to living the way we were meant to.