But then she tries to rationalize anyway. So, I have to answer.
She says this: When I write, I want to tell my story directly to you. I want you to read it exactly as I wrote it... To me, it is the fan fiction writer saying, “Look, the original author really screwed up the story, so I’m going to fix it. Here is how it should have gone.”... At the less extreme end, the fan writer simply changes something in the writer’s world. The tragic ending is re-written, or a dead character is brought back to life, for example. The intent of the author is ignored.
Hobb is starting from a flawed premise. NO author has the power to make a reader interpret the story as the author would have them interpret it. You put your words down on paper, you put your words out there--and you have instantly lost control of them.
Ask people what the Harry Potter books are about, and you'll get a lot of people saying, "It's about this orphan boy who's being educated to be a wizard, and he's got an enemy after him." But you'll also get those whose first response is, "It's about a damaged yet powerful man who wanted to preserve the pureblooded line of wizards, but he went tragically, homicidally wrong." And also, "It's about this guy who's defeated one evil wizard and now his fate is tied up in defeating another, and he's grooming this kid to do the work." And I absolutely know you'll hear, "It's about this tragic hero who followed the wrong side in the first wave of a war, and now, to earn his redemption, he's a spy for the good guys."
When I read The Lord of the Rings, I found myself skipping, actually skipping in Books 3 & 5 in order to read ahead and find out what was happening with Frodo and Sam. I've had discussions with people who did exactly the opposite--zipped through books 4 & 6 to get to the "good" stuff with Aragorn and Pippin. Did the author have control over us? If Tolkien had said, "No, no, you can't DO that!" we'd have replied, "That's your problem, not mine--your book made these characters the most interesting to me."
The author cannot control the reader's interpretations even of her own original work. To take this to the next step, it's even more ludicrous to think that the author can control the reader's imagination.
Why does a writer conceive a story? Because she looks at the world around her and decides what kind of tale she'd like to tell, based on her literary talents and preferences and what she knows of the world--of science and of history and of its stories and of human nature. She uses her imagination based on the world she knows.
Once a writer has put her story out there, that story is part of the world. It too is a basis for inspiration and the imagination of others. Hobb says, A writer puts a great deal of thought into what goes into the story and what doesn’t. If a particular scene doesn’t happen ‘on stage’ before the reader’s eyes, there is probably a reason for it. If something is left nebulous, it is because the author intends for it to be nebulous. But the very act of leaving it nebulous is invitation to the reader's imagination. It's a contradiction to say, "Don't try to think about what it means"--what the nebulous bits mean is, every reader can, should interpret for herself what this means. That is the point of the nebulous bits.
Fanfiction is this: it is extending one's imagination about an existing story into a text medium.
You cannot prevent imagination writing itself in the reader's head. And you cannot prevent some people--those who have the storyteller's disease--from writing down the resulting stories in their heads; for those with storyteller's disease, it's like telling them not to sneeze. (No, better--for those who believe the resulting story is a good thing, think of it as telling a laboring woman not to push. For those who hate the stories that result, imagine it's like telling a person not to vomit.) Those who think of writing only as work may not understand this--those who have felt what I call "the frenzy" know exactly what I mean.
So Robin Hobb, like many authors, does not like to see people messing with her babies. That's fine. No one has to be rational about that or be asked to justify it. And the medium of the internet as a distributor for fanfiction has added a whole new level of complication to the issue--but I'll save that for another time.
But a case against fanfiction can't be argued by saying, "Think only what I want you to think about my stories."