Have you ever seen human skin up close? Or inside of the human body? You are literally COVERED head to toe, inside and out with little worm/bug/bateria creatures. On your skin there is millions of these little bug that can be seen with a microscope. In your digestive tract, it is MANY billions of bacteria, constantly eating your food, and shitting out other food in your body(often as a symbiotic relationship). Your tongue is constantly covered with bacteria, and has more of it than many "dirty" places you can think of.

After a while you get used to it. Even the parasites that are in almost every piece of pork you eat. Even the mites on cheese, that hibernate while refridgerated, then spring back to life, and eat the cheese, then shit on it, when brought out of refridgeration(that's what gives "aged" cheese its taste, and what makes pizza taste so "different", or "better" the second time you heat it). Mom's reheated spaghetti not only looks like a bowl of bacteria and worms. It truly is, but our eyes cannot see it.

Beauty, and Disgust is in the eye of the beholder. Many people lick asshole all of the time in sex, and put their penises in assholes. Humans aren't as clean as some people think.