I think Rowling was trying very hard to avoid favoring her "self-insert" character to the detriment of the story, and ended up detrimenting the story by overcorrecting for it. Hermione can't be right, she can't win, she can't be recognized as competent and capable and justified by the other main characters, because then that's just Rowling applauding herself. I think was her mindset, anyway.

Not that it would have made the story good if Hermione were handled better, because Rowling still just isn't a good writer. But this is one flaw I can empathize with at least. It's a mistake I could see myself making, though I probably wouldn't imply that slavery is good in the process.