It's fine to love a book or movie series. It's fine to hate a book or movie series. And it's fine to be a purist - someone who is not the creator of a fictional world or universe, but who feels they have the right (even, in some cases, the obligation) to criticize a creator (even one of multiple creators authorized by the original creator) for deviating from what the purist feels is the proper direction, narrative or facts of the world or series.

It's also my right to believe non-creator purists are arrogant for criticize any of the creators for violating some canon that the purist feels is "wrong."

In short, I think a lot of "purists" are quite arrogant to think they know better where the fictional universe they did not participate in creating should go or shouldn't go.