I read somewhere that c**t is the most offensive word according to a survey of American women.
I think one thing that makes the c word a bit different than the f word or the s word is that it is just not used nearly as much. In fact, I don't even remember hearing the c word until I was quite old. Yes, I had a sheltered childhood. But I was very familiar with the s word and f word. (I myself am not someone who uses that language but I've never really been offended by it. I was in the Navy, after all.) Anyway, I suppose what makes the c word more rare than the f word or s word, at least in America, is that the f and s words are used as interjections, often with no serious meaning. Usually when the f-bomb is used, it's not meant in a sexual way or even with the intention of insulting someone else. But the c word, at least in my own experience, is usually used with the conscious desire to insult someone, either directly or in third-person.
On the one hand, I can see the point of people who think society is better off when people keep their language clean, especially when children are around, but even when they are not. I'm not convinced we wouldn't be worse off if any word were allowed anytime anywhere. On the other hand, hangups with swear words can be sort of silly, and I admit that I play along with it. For instance, I don't use the s word, but I have no problem saying 'crap'. They mean the same thing, of course, but one word is not to be used in polite conversation and the other can often be used almost anywhere. Most of my friends are about as clean in their language as I am, and I don't know any of them who are afraid to use 'crap' in conversation. I think it's also interesting all some words are taboo in one part of the English speaking world but not another, such as shag. And of course there are the words that can be totally G rated with one meaning and vulgar with another. There's nothing offensive about talking about a nurse who happens to prick the finger of my friend **** or a farmer who wakes up with then **** crows, but use those words with other meanings, and moms will want to cover their kids' ears.