Maybe Harry thinks fanfiction often distorts the real relationship between him and Ron. He values their genuine friendship and doesn't like the fictional and sometimes over - the - top interpretations in fanfiction.
In some fanfics, the relationship dynamics are deliberately changed for the sake of creating drama or exploring different storylines. So, the author might have made Harry not like Ron to introduce conflict. This could involve things like Ron being too overbearing or not understanding Harry's needs as much as he should in the fan - created scenario.
Well, it could be that in the fanfiction, Ron made a mistake that had long - lasting consequences for Harry. Maybe Ron accidentally revealed one of Harry's big secrets that put Harry in danger. So, Harry is unable to forgive Ron as it has changed his life in a negative way.
Perhaps there were some secrets that Ron was keeping from Harry. In the wizarding world, secrets can be a big deal. If Ron had a secret related to his family or some other important matter and Harry found out about it in a way that made it seem like Ron was hiding something bad, it could lead to Harry not trusting him. Also, Ron's friendship with other characters might make Harry jealous or suspicious. If Ron was getting closer to someone Harry didn't trust, it could spill over and make Harry question Ron's loyalty to him.
Well, in some fanfictions, the author might want to create an alternate scenario where Harry has different relationship dynamics. Maybe they want to explore other pairings for Harry and so they write him as not liking Ginny to deviate from the original storyline.
Maybe in those fanfictions, the author portrays McGonagall in a way that Harry doesn't like. For example, the character might be out of character and act too harshly or differently from how he expects her to be in the original story.
It could be that Harry has a very specific and personal view of Mcgonagall. The fanfictions often add a lot of fictional elements that deviate from his own perception of her. For example, they might make her act out of character in terms of her strictness or fairness, which he doesn't like.
Maybe in some fanfictions, Dumbledore's character is portrayed in a way that Harry doesn't like. For example, if the author makes Dumbledore overly controlling or having some hidden motives that are against Harry's interests.
Well, it could be that Harry has such a personal and intense experience of Hogwarts that he doesn't like how fanfiction can be so varied and not always in line with his own memories and feelings. He might feel that the real Hogwarts story is already perfect as it is, and fanfiction is just an unnecessary addition that doesn't capture the essence. For example, he might not like how some fanfictions change the relationships between characters or create out - of - character scenarios for his friends at Hogwarts.