Why is cursing bad? Why is foul language looked down upon, censored, considered uncouth?

OK, there are religious commands that forbid "taking the lord's name in vain", and out of respect for other's sensibilities and faiths, it is only good manners to limit that kind of speech. But why should it be illegal or offensive to use plain, colloquial language to describe common sexual terms or bodily functions?

We all shit, piss, and fuck, and the ass, prick and cunt are all intimately (pun intended) involved in these activities. If your upbringing has made you overly sensitive with the common terms, why should we go to the trouble of substituting medical euphemisms?

It is no big deal for me to limit my use, like I said, it is common courtesy, and some people's offense at these terms should be respected. After all, it isn't polite to say "nigger" either, especially when used as a deliberate insult. If I were black, I certainly would be offended, and I would be justified in taking it as a deliberate insult. Even in re-establishing my dignity with a good punch in the nose.

But shit, man. For grown men and women to be talking about "the n-word" is fucking ridiculous.