This is a debate that is touched on heavily in the wonderful documentary The People vs. George Lucas (2010) (on NetFlix the last time I checked) which seeks to explore how both creators and consumers can stake a claim to art. But something recently has resurrected it for me.
Bill Watterson, the reclusive creator of Calvin and Hobbes, was famously protective of his work, refusing any and all merchandising deals in the name of not cheapening what he considered to be his art. Due to an increasing pressure to fit within shrinking panel constraints, and to merchandise his work, Watterson stopped production of Calvin and Hobbes in 1995. Because of the popularity and almost universal appeal of Calvin and Hobbes, there has been a massive call for Watterson to resume work, or to at least give his fans something, pleas that have gone ignored. Recently Slate revealed that a documentary on Calvin and Hobbes is in the works, bringing (unfortunately) Watterson back into the spotlight.
I tend to agree with the creators of The People vs. George Lucas, in that at some point the ownership of art passes from the creator to the consumer, at least in part. Creating for me is not a monologue to be spouted and left alone, but a relationship with a continual back and forth. Even though I do create these works and these characters, at some point they cease being my progeny and exist beside me. Like a lover I cannot hope to control the influence they have on other people (or the influence other people have on them).
Thus I don’t really understand Watterson’s perversion of purism, although I can certainly respect both it, as his right, and his consistency on the topic. I’m not sure it would cheapen my characters to see them plastered on merchandise, and I’m not sure if it would anger me if I felt that someone was getting them wrong. It might disappoint me a little because if a character is easy to misinterpret, (and I don’t think they should be in most cases) that’s pretty much entirely my fault and my failure as a writer.
A lot of people roll their eyes at fan-fiction, especially slash fiction, but to me that’s the ultimate compliment. That someone could love one of your characters enough to want to further their existence (or love them enough to want to vicariously fuck them through the written word) is amazing to me.