> This post floated into my head a few minutes ago, and I thought about it and realized something: you may think it's wrong to kill people, but I don't think that would make it wrong for you to write a story where a character killed someone.

This is true, but as an analogy to including profanity in one's writings, I don't think it holds. To write about a character committing murder, you do not have to commit murder yourself. To make a character swear, however, you have to swear yourself.* Consequently, I don't think the analogy applies.

(*Unless, of course, all you write is, "He swore," without writing out the exact line of dialogue.)