I can see your whole point around this, and it would make sense except for… Occam’s razor?
Ok, not quite literally the same principle, but something similar…
Think of a long lane, like a bowling lane, and it has a hole in the middle.
You can throw your ball there and hit the pins at the end, and you score points for that. Or at least you assume you do since the scoreboard is too high for you to see it.
But every now and then the ball falls onto that hole in the middle.
Now you turn to me and say “I think that hole is like ‘a bug’… I mean, the ball would reach the end much easier without it, so that hole is something bad which needs to be fixed”.
Well… this might make sense within your limited perspective… but what if when you look at the scoreboard you would see that when the ball falls into that gap you score the highest points!
Where I am trying to get here?
Your conception that deviant sexuality is “a bug that doesn’t help propagating the species” is entirely dependant upon the assumption that we have an inherent purpose of propagating the species.
Such assumption not only makes everything a lot more complex than needed (hence the Occam’s razor mention), and not only it’s unprovable…
but it’s opposite argument can actually be made with a lot less effort.
Take a look back in history.
The moments where we have any “your duty is to have children” argument recorded is paired with the need for controlling resources by the ones recording/enforcing it.
I won’t point fingers at any faiths because that would derail this topic, but…
There are dozens of examples where When a population was being prosecuted by someone else their priests begun enforcing “you must have more children”.
When distinct faiths needed to contest control over a territory the winner was the one with stricter “women must bear children” rules being created
When churches begun raising into power they needed more followers for political/strategical reasons, so they begun banning homossexuality…
I find it disturbingly coincidental that the same people who tried to push this belief that “we are put on this world to have children” (be it religiously or “scientifically”) were always the same ones who benefit the most from their culture having more children.
Do you think humans enjoy being raped?
You just gave @Coma 's argument a point there.
If sex was a mechanism to propagate the species it wouldn’t be so tortuous…