On the taboo subject. It's about vulnerability. When we're pooping, we're vulnerable. When we're mating, we're vulnerable. The most successful/efficient species have some leisure time  to mate. You can't mate if you're always on the run from predators, or always eating. Also, human offspring are vulnerable for longer than any other species.  For them to have protection, the parents have to be capable of bonding with each other and other humans. A great deal of that happens because of emotional vulnerability during mating. So there are societal taboos against letting that part of ourselves be out there for anyone to damage. The privacy of our most intimate moments is evolutionary protection.