Really, I don't think the point of this thread was to discuss whether homosexuality is right or wrong, but since everyone else is I think I'll add my 2 cents.
Homosexuality is unnatural and that makes it wrong in the greater majority of the human population's mind...
Just to counter a point, Homosexuality occurs in nature as well as in human society. There's nothing unnatural about it. It would be like saying that albinos are unnatural.
Strictly speaking, homosexuality is natural like albinos, as Harisenbon pointed out. That being said though, albinos become albino because of a gene defect or mutation. Albino animals have a much lower chance of survival in their natural environment because they lack camouflage (& therefore protection). They are sometimes born with other defects such as impaired hearing or vision. So as a matter of survival, being an albino is a disadvantage.
I think homosexuality too, from mother nature's point of view, doesn't really serve any purpose. The whole point of life is to propagate life. Being homosexual kind of limits one's reproductive chances. So, I guess whether homosexuality is natural or not depends on one's definition of "natural".
I don't think negatively towards gay people (some of my friends are gay), I just don't think really think it's "proper" (sorry, I don't know what other word to use) - scientifically speaking.