People who don't swear scare the fucking life out of me.
I don't, except in circumstances where I'm deliberately trying to shock, or at least surprise. It's not a matter of "repression", it's that profanity is not part of my vocabulary. You assume that people who don't swear are "repressing" or "censoring" themselves, but that assumption presumes that they actually do swear in their internal dialogue, but then don't say it out loud. But I don't use profanity in my internal dialogue, either, though I suppose I have some stand-in words (dang, etc.) which fill more or less the same purpose.
To put it another way, a good friend of mine like to say "If you don't scream FUCK when you hit your thumb with a hammer, your head will explode." My response is "When I hit my thumb with a hammer, I'm in way too much pain to go to the effort of remembering to scream FUCK." He's assuming that the curse word will be naturally present and that if you don't scream it it's because you're holding it back. For me, the curse word just isn't there, so what happens when I hit my thumb is a wordless howl of pain. No repression involved, and my head remains intact.
In addition, I think profanity is generally counterproductive. Rather than saying that something is "fucking stupid", why not spend two more seconds thinking, and articulate why it's stupid, or what about it is stupid? Your phrase accomplishes exactly nothing other than to make people understand that you're angry. It conveys no other information and does nothing to rectify the stupidity. Also, it's pretty common that when people bother to think about what exactly it is that's making them mad, they discover that, in fact, it's not stupid and that they just hadn't thought the whole situation through.
Finally, I find that the fact that I hardly ever use profanity makes it a really powerful tool on the rare occasions I do choose to use it. Those who use it constantly have basically nowhere to go when the situation deserves a really strong statement.