To further support homoloveuality/aloveuality being unnatural, (I have nothing against either) you should pretty much see that humans are built with instincts to survive, part of that being to reproduce. You can't exactly keep your species going if you're not getting a female pregnant/getting pregnant from a male.
Again, I have nothing against either homoloveuals, aloveuals, or anyone else for that matter. I am just stating something that I think makes some sense.
The explanation may seem pretty simple, I know, but some people just need a reminder.