Well, **** stinks, of course, and that's a good thing, because it would be bad for your health to be surrounded by ****. People who routinely and carelessly shat upstream from where they took their drinking water didn't have an evolutionary snowball's hope in Hell. I read somewhere once that when little baby prong horn antelope ****, it comes out in a little sac which Mom can then remove, so that the aroma doesn't attract predators. This doesn't need to go on for very long, because those goats (yes, prong horns are actually goats) can run like the wind, and very soon after being born.
Seriously, though, that scatalogical functions are viewed with distaste could well be an evolutionary product which protected our young from predators, and our water supply from stupidity. As for sexual functions and sexual organs, i blame religion. After all, if you can control someone's sexual urges, you can't really achieve anything greater in the way of dominance.