Again, does natural always equal right? No.
Fair enough. So the people who argue that homosexuality is wrong have a valid point then? The few who acknowledge that it does occur in nature, I mean.
1. Some non-human animals exhibit homosexuality.
2. If a non-human animal does something, then humans shouldn't do it.
3. Therefore humans ought not be homosexual.
1'. Some non-human animals exhibit altruism.
2. [As above.]
3'. Therefore humans should not be altruistic.
The unsound premise is (2.), i.e., that humans shouldn't do anything that non-humans do.
In general: something may exist in nature, but that fact tells you nothing about whether it's right or wrong.