Everyone shits, but "shit" is still considered a bad word because of its material properties. Fuck, on the other hand, is something everyone loves doing, except when done by force... I guess the reason it's still seen as a bad word rather than a "love word" (besides old religious believes that sex is actually intrinsically bad, which some people might still hold) is that "fuck" is unconsciously associated with forced sex (rape, to be clear) while consensual sex is associated with other words/phrases like "make love", "intercourse" etc. which do not have the same bad connotation.
I think the "old religious beliefs" have more to do with it than any connotation of forced sex (at least I have never recognized this in the way people use the word).
"making love" is something partners do as a healthy and (re)productive part of their relationship, "fucking" is what 'animals' do, purely done for pleasure. It is a bad word for the same reason gluttony, excessive alcohol and drugs are a sin. A society where everyone mindlessly chases dopamine from carnal pleasures is less productive, especially when this leads to unrest and violence (and I guess that's where forced sex comes into play).
Near-universal approval and near-universal distaste. A curious phenomenon, isn't it?