Do you have a position on fanfiction? Fights between authors and fans insistent on this activity are ongoing. See Lee Goldberg versus Cathy Young.
The latter, a fanfiction writer and a columnist at Reason magazine, who like all fanficcers, defends this unauthorized use of copyrighted characters, which frankly, are used in bizarre ways, some openly perverse. A handful have translated this activity into book deals. What say you on the matter? I'm with Goldberg: it's illegal and stealing. Even if authorized, it's tacky and pathetic. Write your own and take your chances. That's the honorable way to write.
I don't care what you write.
I don't care if you use Mr. Monk in unspeakable ways or give Darth Vader a sex change operation. I don't even care if you have Jack Reacher get in touch with his feminine side and start shooting pink bullets (Oh geeze, I just heard Lee Child faint dead away). Keep your hands off John Rain of course, but even then...I don't care.
I don't care as long as you don't try to publish it, sell it or send it to me. What you do in the privacy of your own den of iniquity concerns me not one bit.
In fact, some of the fanfic stuff is probably a good writing exercise.
Where the monk leaves the monastery and the rain falls off the plane is when you take these little exercises out for a public stroll. It's one thing to be inspired by Lee Child, Barry Eisler or Laura Lippman; it's another thing entirely to start writing about Omar's backstory in Charm City.
I can't sell that stuff and I'm not much interested in derivative work. I don't read it (but I know Miss Genoese does so it must have some sort of redeeming value) and I reject it instantly so from my perspective it's a waste of time. That more than anything else is why you shouldn't bother writing it if you want your work to be published...and thus fanficced itself one of these days.