Hmmm. I agree with you that that can be really problematic, but I think the problematic thing is the denial rather than the fixing-problems aspect? Like, for example, I desperately love The Dark is Rising books, and I am eternally grateful to Susan Cooper for having written the things, and if I were ever to write fanfic about them it would be because there is this aspect of Silver on the Tree that I think is really fucking stupid and poorly thought out and out of character for everybody. She had every right to do it and it's canon, is the thing. I feel that as a reader I have every right to think it's stupid and rewrite it in my head or elsewhere as much as I like, as long as I don't forget that, or that my version is critique and not what she had in mind, because if I were going to actually try to fix it in the actual text I'd need to be reading it in manuscript and arguing with her pre-publication.

I think it's perfectly valid to feel betrayed by a canon, when it's been going along brilliantly and then something happens that is just like, what the fuck happened to the writer's brain. Because writers do fuck up, and there's a difference between that and the writer making a decision the reader doesn't like. Things like, text has been having great women and then suddenly for no identifiable reason they all have no agency and wind up in various refrigerators, that feels betraying. (Whether it really is or not is another question entirely.) But denying that it happened in canon, which is denying the writer's right to make these decisions, that I think is where the crazy happens.