Right. I understand.
So homosexual acts, in and of themselves, have no benefit to the species.
Once again, evolution is about populations not individuals. It makes no difference really. The fact remains, homosexuality seems to be an emergent biological trait and it has been preserved by natural selection (whether it is purely genetic is uncertain, as there are research that suggests a more epigenetic explanation from causes in the pre-natal phase). Now it is part of our human species.
Again. The homosexual act itself, has no benefit. Is that right?
Seriously, how difficult is this to understand? You seem to be insisting that the homosexual act between two homosexual individuals itself has to directly perpetuate the species. That is not evolutionary theory works. Obviously the sex act (acts really, there is an one sided focus on male homosexuality on TOL) itself does not directly perpetuate the species, that I really hope you already knew. Their acts are a mere expression of their attraction to the same sex. It makes no difference to evolution whether the evolutionary benefit of a trait is direct or indirect.
I believe that sex outside of marriage is immoral.
I do not believe that two people of the same sex can be validly married.
Which of those do you disagree with?
The second one. The definition of what constitutes marriage is historically and culturally contingent to say the least. So many today think they are engaging with sometimeless institution, but if you look at what people say about marriage today it is mostly a mixture between the ideals of Romanticism and Elizabethan England. There is not even a singular biblical understanding of what a marriage is. I see problems with altering that definition in light of a changed perspective on homosexuality in current human knowledge.
Now please answer the question you have been asked so many times. Provide a moral argument for immorality of homosexuality. The above is not that, those are two statements of belief.