Dear professionally-published authors who despise fanfic of their own works,
So you despise fanfic of your own works. It revolts you on a visceral level. Okay. It would be rude and pointless of me to suggest that you shouldn't have a gut-level emotional reaction, because, after all, it's gut-level. And I may even sympathize or agree with you.
But because you are a thinking being, you get to choose what you do, as opposed to how you feel. And in that respect, I suggest you should do the following:
- Say, "I do not want fanfic of my own works to be written. In any event, it would be unwise of me to read such fanfic, so if any exists, please do not tell me about it.";
- Don't read any fanfic; and
- Sic your publishers on any fanfic of your works that is being published for the fanfic author's own profit (an extremely rare occurence).
Because here's the thing about non-commercial fanfic: you can't stop it.
With regard to the practicalities, fanfic is not, as a category, illegal in the United States. Anyone who says otherwise is misinformed. (A useful resource is the Fair Use Overview of the Stanford Copyright & Fair Use Center; see also this 11th Circuit decision about The Wind Done Gone, "a fictional work admittedly based on Margaret Mitchell's Gone With the Wind.") Thus, your legal rights may not be clear-cut with regard to any given story.
(NOTE: I am not hosting a discussion about the legal status of fanfic, because: (1) I've seen more than enough prior instances of it; (2) I don't have time to moderate it; and (3) not to put too fine a point on it, but: I'm right.)
But even if a particular fanfic comes nowhere close to fair use, the Internet is such that—between anonymous posters, pages not indexed by search engines, restricted-access sites, and the like—trying to get and keep that story off the net could be an enormous investment of time and resources on your part, with little guarantee of success. Not only that, but if people hear that you're suing a fan who wrote a non-commercial fic, they're likely to start writing new fanfics in response. I'm not expressing an opinion on the propriety of that, just pointing out that it's a genuine possibility.
More fundamentally, if people are writing fanfic about your works, then their imagination has been sparked by your works; they have been moved by the same impulse to engage with a story that runs through all of human culture. People gossip about their favorite characters; become fascinated by unexplored characters, locations, histories, themes, implications; imagine what would happen next, or if, or instead; and critique every aspect of a work. Sometimes this takes the form of passing in-person conversations, sometimes of blog discussions, sometimes of scholarly works, and sometimes of stories. (Sometimes, even, of critically-acclaimed, award-winning, professionally-distributed stories.) I would be astonished to hear that your own writing never was influenced by this impulse—I say this not to suggest that you've been writing fanfic all along, but to point out the strength and universality of this impulse. (For an eloquent and lengthy discussion discovered just as I was about to hit "post," see Jonathan Lethem's "The ecstasy of influence: A plagiarism" from a few years back.)
You can be revolted by the idea of fanfic of your own works. But you are so unlikely to be able to stop it that you are better off saving your time and energy for other pursuits. Put your position on the record as above and then do your best to ignore it.
Finally, I particularly urge you to not revile fanfic on the grounds that much of it contains sex [*], when your own works, first, are full of sex, some of it involving characters not of your own creation, and, second, were inspired in part by Dr. Who. Because not only have you insulted some vocal fans of your books, but you look a bit foolish to boot.
[*] ETA: a response from the author in question.
ETA 2: the author has deleted the posts in question; the text is archived here.