Jo asked yesterday what I think of fanfic, or people who write stories set in another writer's world usually without permission. It's actually a complex question when you get into it.
My knee jerk reaction to such people is: Don't you dare!
But then, this is followed by a second knee jerk which is: Wow, am I that popular? Great!
On one level, I think it is a good exercise for a beginning writer who can practice in someone else's creation, with characters already extant, so they can just concentrate on telling a good story. Nothing wrong with that. If a writer doesn't then move on to their own creation, well...hmm.
Books set in some worlds, of course, are created by more than one writer. Star Wars books, for example, have many different authors, each commissioned and paid to write a book by those who hold the rights to the world and characters. That's a commercial agreement, absolutely legal and very successful. Nothing wrong with that.
Sometimes the estate of a deceased writer, or an aging writer her/himself, will agree to have their stories continued by another. Once again, a commercial agreement, absolutely legal and possibly successful. Nothing wrong with that, either.
So when would it start to upset me, assuming that someone some day will use one of my worlds and my characters?
Fanfic writers swop their stories. Sometimes they take your characters down roads they were not intended to travel - some write porn, or change the sexuality of people in your books, or who sleeps with whom, or make other major changes. That's where I would be upset if these tales were open to anyone who happened that way. If they stayed on egroups, newsgroups and mailing lists and such, I wouldn't worry too much.
I doubt that I would actually do anything about it, but I wouldn't like it. Why not? Because I love my characters and my worlds. I expended a great deal of effort to make them what they are, and it would hurt to see them used this way.
Why then would I not do something? Not worth the trouble. Every creative person has to shrug and accept that their creation - when it be music or an artwork, or a play, or a designer dress or whatever - may end up being treated in a way they don't like. Comes with the territory. Live with it. At least they presumably bought your books and read you avidly enough to mess around in your world!
When would I take action? Well, my publishers and I would be most unhappy if someone took my creation, used it as background to their own work, and flogged it to make money for themselves. Now that would make me really, really mad.
I am no lawyer. This post is purely about my personal reaction, and why. If anyone wants to know just what is legal and what is not, try this site.