Y'know, I actually had a conversation with my sister (who is going into college as a linguistics major) about this last night. Namely, there is a certain emotion that saying Fuck or ***** conveys that you cannot convey with other language. There is a sense of anger that isn't really present in other words. For example, the ostensible definition of "fuck" is "to fornicate". Try shouting "TO FORNICATE" next time something goes wrong. Or tell someone to "fornicate off". They're a valid choice of language specifically because of that emotional undertone. All my life I had my parents telling me "if you can only use swear words you're just not clever enough to come up with something better", but that's just it: I am clever enough to come up with something better or more original. I could call someone a lice-infested pile of bovine excrement, and it'd be original. But it would not have the same feeling as saying "you're a piece of shit."
I dunno, I agree that there's a stigmatism that exists simply because we're told they're bad, but at the same time if they weren't considered to be foul language they wouldn't have the same effect. It's a kind of ouroboros situations, I suppose (I refuse to say it's chicken and egg because that one has an obvious correct answer).
EDIT: also, the whole "Fornication under command of the king" thing is just an old wive's tale. It's just fuck, plain and simple.