The sense of disgust is a fascinating and clever adaptation in the brain that functions like a beneficial phobia. It causes people to avoid things that are bad for them even though they don't know intellectually why they should avoid them. For instance, bodily functions are disgusting to us because they are toxic to us or because being unclean in general triggers our sense of disgust. That's why even primitive peoples usually bathe regularly; it's an instinct based on disgust which allowed humans to avoid germs millennia before we knew what germs were.
People who have higher intelligence tend to have higher levels of disgust, or lower tolerance for uncleanliness, sometimes to a degree that seems illogical, as if the disgust sense is going haywire. Tesla couldn't stand having overweight people work for him. Some will only eat white foods because anything else is "dirty".
Sometimes there is a benefit to seemingly random aversions. I know someone who dislikes drinking opaque liquid since he can't see what's inside it, and only eats his food dry because sauces, dressing and such gross him out. He has a natural aversion to pork and seafood, despite having never been near a Jewish person. You can see how these would actually be useful aversions to have in a natural setting, eating unprocessed foods.
Much of this thread talks about morality in conjunction with disgust, but I find that the kind of disgust that most repels people is always of a squishy or icky nature. We may disapprove of someone's morals, but we'd much rather hang out with them than with a friend who we admire but who hasn't bathed in a week or washed their clothes.
