As a writer, I am often confronted by the choice to add the "bad" words, or not to add them. In the real world, I occasionally use them. I do take my audience and the situation-- professional or casual for instance, into consideration.
Of late, I have read several discussions about Young Adult fiction and the language it contains. I think it is a whole other question, though, when we consider books for adults.
I take my approach in the written world, just like in the real world, and consider the target audience and my characters, then determine just how potty mouth they will be.
I ask this question: Does it serve a purpose? Does it lend believability to the story, or make the character more alive to the reader? Otherwise, I can leave it out; profanity for the sake of profanity doesn't work in my writing. But, I also think of the opinion shared by a good friend and University professor, Cemil Tarhan, that there are times when profanity is called for; times when it affirms the authenticity of the moment, conveys the harshness of the exchange or thought, truly brings home the anger, incredulity, or even humor in your character's situation.
There are times when no other word suffices, and if you omit the profane, or substitute a lily-white word, your written work is diminished by the censorship you inflict on your story.
There are a couple words that I just don't use when I write. A personal preference? Perhaps. But, mainstream fiction is full of bestsellers whose authors had no such hesitation.
Let me say here, on my facebook profile, it does list "truckdriver" as one of the languages I speak...even so, I am keenly aware of context when using base language in a story. Sometimes, even though a word might be anatomically correct, it taints my opinion of a story--even my opinion of an author. And there are times that base words fit. An example of what I mean--Audrey Niffenegger writing in The Time Traveler's Wife her protagonist after giving birth "...and my cunt hurt." A book that I thought was pretty good, but would much prefer she had used another term, and have wondered why she made the word choice she did. After speaking to others, I realize that my reaction to her choosing to use that particular word is not an isolated case. It has tainted my opinion of her and might even affect my future Niffenegger book purchases. BUT...in Sarah Gruen's Water For Elephants, when the protagonist said the word, "fuck", it fit, it worked. I thought it was critical to conveying the emotion of the moment.
I don't think that there is a formula, or a rule of any type to determine word choice. For me, it comes back to knowing your target audience, and what will be well-received. And working toward an impression readers take away from your work--either leaving them with a zeal to read more, or driving them away.
But, <smiling> if any of you have rules by which you govern profanity in your writing, please share. I never stop trying to learn.
If you have an opinion-- supporting or counter to my own expressed here, please share your thoughts.