Will Smith don't gotta cuss in his raps to sell his records
well I do, so **** him and **** you too
- Eminem, "The Real Slim Shady"
This was the first thing I thought of when I saw this thread title, and you know what? I think I can see where Slim's coming from. Writing lyrics is harder than most people think it is, and a single word can change the tone of an entire verse. Some artists put swear words in their songs because they feel that those are the words that can most effectively convey the message that they're trying to get across.