There is a debate on the letters pages of the current Writing Magazine about the use of swearing in fiction. On one side is the argument that many readers find it offensive and that it is unnecessary. On the other hand it is argued that this is how many people speak; that in the real world one hears swearing all around and it is unrealistic not to include a lot of swear words if the character in question would use them.
Perhaps it is not entirely true to life to leave out the swearing, but how often do we write dialogue that is entirely true to life?
Some people use a lot of ums and ers in their speech. Do we include all of those?
What abut the person who ends every sentence with 'know what I mean?' or, like, says 'like' two or three times in every sentence, like?
People often pause in the middle of a sentence while they search for the correct word, or a name they cannot quite recall. Do we include dashes or ellipses every time that happens?
Sometimes, a speaker will have to repeat what he or she said because the other person did not hear properly the first time. Should a writer include instances of that, for the sake of realism?
Some people's speech is very disjointed, jumping from one subject to another and taking forever to get to the point. 'I saw that woman yesterday, you know the one, lives next door to the shop - did I tell you there are new people in the shop? Nice couple, got a little boy. Anyway, this woman - oh, you remember her, her daughter was a year above you at school, Sally or Sandra or something, went to train as a nurse, anyway, like I was saying -'
Most people probably know someone like that, but would we write her speech out exactly like that?
All of these examples have the effect of slowing the pace of the story. A writer might choose to use each of them at one time or another for a particular purpose, but it would be to serve the story, not for the sake of realism.
Excessive use of swear words similarly slows the pace. Yes, some people in real life do use the f-word multiple times per sentence, but in fiction it is repetitive and boring. Why would any writer want to bore his or her readers?
Where the author has a word limit, repetition is also a waste of words.
And to return to the original point, many people would find prose littered with obscenities and profanities offensive, and not want to read it. Why would a writer purposely write in a style that he or she knew would offend a proportion of potential readers?
Of course, writers should not avoid challenging or controversial styles or themes for fear that people might not want to read them. But use of bad language does not fall into this category. A good writer should be able to find other means of establishing character or mood. A professional writer should be aiming to entice readers, not alienate them.