There were heroes who came from “common backgrounds’, but just as they emulated the honor and courage of legendary heroes, they also assumed their manners. They may have come from longshoremen and mountain men, but they never swore. You can see this in some of the old movies when the hard bitten detective is clearly about to swear, but remembers there is a woman present (shown by a flick of his eyes in that direction) and stops himself.
Then Hollywood decided that if they were “slew the dragon” and saved people, it was OK for the hero to be true to his common roots, and we ended up with (as it’s the season I’m thinking of Christmas movies) John Maclane in Die Hard and Martin Riggs in Lethal Weapon, where the “f word” comes out of their mouths every five minutes. I guess they just figure that anyone who that sort of language bothers can stay away from the movie.
Just as the “whore with the heart of gold” never got the guy (she often ended up sacrificing herself so that the man she loved could make his escape with the pallid virgin), the cruder male characters couldn’t aspire to winning the virtuous leading ladies. These days, they get the “consolation prize” of lots of great sex, again the implication being that that’s the best thing they can imagine, rather than all that they deserve.
It’s true that different subcultures have different expectations, and the dialect that you were taught as a child does not indicate whether you’re a good guy or a bad guy- even if it does determine whether you are socially acceptable in other subcultures. And we can be assured that the “lower classes” are just as suspicious of the motivations and outcomes of dealing with rich folks as the rich are as likely to assume lower intelligence or morals of the poor. No matter where you come from, the “Other” is suspect. Language is simply one mark of difference, and one (as we see in Pygmalion or My Fair Lady) that is not as easy to change as a suit of clothes.
Modern theory has it that swearing is a mark of a person being honest. But we need to step back from Philip Marlow trying hard to be the man his mother wanted him to be, and remember that we grow where we are planted. When Willie the Pooh says “Bother!”, it’s not affected, it’s simply what comes out of his mouth when he’s upset. Yes, we need to remember that because someone swears, that doesn’t make him a bad person. But at the same time, we need to remember that just because he doesn’t, it doesn’t mean that he’s repressed, dishonest, or there’s something wrong with him.