I think it's fine to point out the differences and critique, etc, it's all part of being really into something.

The only thing that bugs me is the way some people feel their role is to 'educate' the rest of fandom about canon. (You know, the kind of people who leave comments on kink meme prompts saying 'x isn't possible because of x in canon'. 'Cos, I must have missed the bit where Tolkien described how they all went at it like bunnies...)