For me, it all boils down to what the show gives us as guidelines for the characters. L&C never crossed into profanity. (Note: I do not consider "hell" and "damn" profanities.) So, when I write, I ask myself, "does this actually sound like the character?" While it was mentioned that Lois cursed up a blue streak when she broke her ankle, we never actually saw swearing occur on screen.
Now, if I were to be writing for, say, Dexter, I would have Deb dropping swear words left, right, and center - because that's how her character was. Every other word out of her mouth began with the letter F.
Writing "Gosh darn it!" for her character would not be natural and would not ring true for the character.
As a reader, I will not read a story in which the characters sound "off." If Clark drops an F-bomb, I'm not longer interested in the story, because the author does not understand the fundamental truths of who he is. And if, in the case above, Deb has a squeaky clean mouth - that writer doesn't understand that character either.
I do take offense at the idea that (and I'm paraphrasing here) people who swear have a fundamental lack of command of the English language." I can swear like a truck driver in the privacy of my own home, but I would never do so in a professional setting. And I think I have a rather decent, if not impressive, command of the English language (as I sincerely *hope* my stories demonstrate). (I'm trying to work on the swearing thing before my girls get old enough to repeat what I say.)
