I'm in agreement with your points I've snipped out. Homosexuality is obviously biological
However the above isn't true. Evolution works at the level of the gene and the individual not the group. Gay people can reproduce just as well as straight people and often do. For what you suggest there'd be no need for these individuals to be gay - just infertile... but as I say its not how it works
Let's put it this way: You have tribe A which has no gay members and no gay genes in its library.
While tribe B has some gay genes in its library, even if those genes are not passed on by the actual gay members of the tribe, they are carried through and the tribe occasionally produces a gay member.
Let's assume that tribe B's % of homosexual members proves to be a major advantage and they hunt, gather, and become extra supports for the tribe's offspring, keeping them well-fed and safe.
Tribe B increases in size as more healthy off spring survive ... genes for those characteristics remain in the group. The group's genetic influence grows, and spreads.
Meanwhile, tribe A shrinks, and ultimately fizzles out due to a failed group strategy.
The result is that the genes from tribe B become are dominant in the species, while the unsuccessful tribe's genes disappear.
Evolution is about survival of the fittest.
In individual organisms that's about survival of the fittest individual and his/her ability to reproduce. In groups, it's about the group prospering and spreading influence and genetics - each member of that group does not have to reproduce for that collection of genetic code to keep spreading and moving forward.
So, by that logic, it is perfectly reasonable to conclude that homosexuality could be an evolved-in characteristic that benefits the survival of a group.
We are not single celled free-floating amoeba, we are a hugely complex interconnected social organism that functions as cooperative groups, so evolutionary mechanisms become a tad more complex than simple generational progression (although that also still happens).
We don't just carry the genes that produce a single copy of ourselves, we also carry a huge library of other options that may not be expressed in ourselves, but might reappear in our offspring when our genetics are crossed with the other parent's genetics.
So, other features than those presented by the parent can crop up in their kids. That could be a huge advantage, could produce fairly random results like a % of redheads to non-redhead parents, perhaps gay offspring or, it can go horribly wrong and you get two carriers of a genetic disease like CF who don't have any problems themselves, yet produce a kid who does.
I don't know exactly what the evolutionary advantage to a tribe of having gay members might have been. It could have been stronger supports for the group, it could have improved social cohesion within the tribe, it could have been anything. Whatever it was, the characteristic seems to have been around for a very long time, and be very widely distributed right across the whole human species so it's obviously been something that we have had in our make-up for a very long time.
Also, yeah of course gay people can reproduce, but if you're attracted to the same sex, the opportunity to do so is a little more limited.
All, I am saying is that the whole notion that it's some kind of evolutionary error/hiccup or that it's unnatural does not really stand up at all.