SF classic author Isaac Azimov had a character named Hari Seldon (The Foundation series) who invented a science called 'psychohistory' which was the science of predicting the behavior of large populations.
This is irrelevant, except to introduce one of Hari's favorite sayings, which was: 'Violence is the last refuge of the incompetent.'
I have my own version: 'Profanity is the first refuge of the inarticulate.'
Now, if you have an inarticulate/asocial character, then profanity might be perfectly appropriate, but there are more subtle and effective ways to show that kind of character. It's also appropriate in a military type setting, but not to be overdone or it becomes distracting (like too many erotic scenes) and of little use in advancing the story.
In everyday language profanity has become common, and so, you might argue, I'm just reflecting the norm of the culture. Really? Since when is dialog just conversation? If I want to experience an expletive filled conversation I'll have lunch at the nearest truck stop, I don't have to read your book for it. Profanity is nothing more than a one-word cliché, a cheap device to make a character or situation seem 'edgy.' But it is just as much an evasion of your responsibility as an author as any other cliché.
My characters do spout an occasional 'damn,' 'c**p,' or even 's**t' as an exclamation in the appropriate circumstance. Indeed, there are places where if you don't use one of those words (the plane is about to crash into the mountain, for instance) it would be as unrealistic and distancing as using them in too many places.
Words like that are spices to be used sparingly; least you dull your reader's appetite. An overspiced dish is as unpalatable as an underspiced one. So sprinkle expletives carefully.
BTW, least you think me a prude, I was a Marine, where you can't eat a meal without someone asking you to pass the f...'in salt. True, but once again of no use in advancing a story, unless the story is about how crude Marines can be.
But that's not a story, or even news.
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