So, you've read the theories, seen the evidence of homosexual behaviour in nature, seen the long human history of homosexuality.... and you still call it unnatural?
I've read the theories from both sides of the evolutionists positions, the Churches version of natural law, the opposition to it, and read about the long record of it in history.
1, Evolutionists haven't made a consensus agreement on the issue. I lean to the position that I previously mentioned. Adaptedness is a key component of evolution, reproductive success is a measure of adaptedness.
2, The Churches view of natural law is more moral than functional.
3, There's as much recorded history of birth defects, as homosexuality. You can make an argument that they are both natural, that doesn't mean they follow the natural order of humans. A male and female procreate, to further the species.
Please don't confuse my position for a moral one.