sex is gross
A considerable exchange of saliva, sweat, semen, hairs, or any other body fluids happens during the act. Not to mention the smells emanating from the mouths and skin of the person. Sounds gross, right?
Except when you feel horny. That’s when lustful thoughts of having sex as per your fantasies makes all of this very appealing.
If it wasn't so, humans would have grossed out at the idea of having sex with each other. They would have stayed away from each other as far as possible.
We cant even share toothbrushes, towels, combs, soaps, etc. with our closest relatives and friends. That’s how much hygiene and cleanliness is part of our lives. How do you expect humans to suddenly throw off their clothes and start exchanging body fluids without feeling gross about it? And this is only with the current hygiene and cleanliness standards. Far before the era of modern technology, people wouldn't bathe for days and I don't even want to imagine how they tried to keep their mouths from smelling bad.
It was probably why humans came to possess the unique trait of having sex for pleasure, and without it, we would have been history. For the better or for worse, this trait has been one of the most influencing factor in societal and gender roles throughout history. Mostly for worse.
