I had an art teacher in high school whose catchphrase was "you've got to know the rules before you break them." She was talking about modern art, but it's applicable in many other ways. Despite the fact that ignorance sometimes actually can be a defense in court, I still think it's better for fan works creators to know a bit about copyright before creating and distributing their works.

I've been thinking a bit about my attitude towards derivative works in fandom vs. in academia. Related to the "educational fair use" clause, it's perfectly acceptable in academia (from freshmen writing term papers to professors doing research) to use other people's previous works (no explicit permission required), so long as you properly cite the source and add something substantive to it. I think as regards the "morality" of fan works, I think I have a very similar attitude: people should say where they're getting something from, and they should create their own works and not just copy/steal someone else's work.