I don't approve of fanfiction. An author writes the story she means to, no more and no less, and it's gross impertinence of her 'fans' to attempt to write what she chose not to. Real fans would have more respect. Had Jane Austen wanted there to be a sequel to Pride and Prejudice, she'd have written it herself. Had JK Rowling envisioned Draco Malfoy and Hermione overcome by mutual lust, she'd have mentioned it in one of Harry Potter's seven volumes.
It doesn't help that the standard of writing is generally poor.
My stance on this clarified for me this week, when I was tracking down the last Mary Renault novel I haven't read, Kind Are Her Answers. It's an early one, so not one of her best, but I still want to read it. And I came across links to Mary Renault fanfiction sites. There's no way I was going to visit them, but it seems most of the stories add in the homosexual sex that Mary Renault chose not to describe in detail. Her view on the subject was:
"I have sometimes been asked whether I would have written this book more explicitly in a more permissive decade. No; I have always been as explicit as I wanted to be, and have not been much more so in recent books. If characters have come to life, one should know how they will make love; if not it doesn't matter. Inch-by-inch physical descriptions are the ketchup of the literary cuisine, only required by the insipid dish or by the diner without a palate."
She also, like any sensible person, disliked being pigeon-holed, and having some of her novels on the Gay and Lesbian shelves in libraries like my local one would, I feel sure, have annoyed her.
Yes, I know Shakespeare based some of his plays on other people's plots, using the same names. That's no excuse for us lesser mortals. Some writers argue that copying another's work is acceptable as a means of learning to write, like using training wheels on a bike. But a bike doesn't have an opinion on the matter, whereas most authors do. I'd certainly hate my characters to figure in another person's writing, and behave in ways I know they wouldn't.