In fanfiction, Naruto could hate Sakura due to her treatment of him. She often overlooked his feelings in the original series. Fanfic authors might exaggerate this aspect. For example, if Sakura continuously dismisses Naruto's achievements or makes him feel inferior, it can build up to a strong dislike or hatred in the fan - created stories. Also, some fanfictions might explore a darker side of Naruto where his pent - up emotions turn into hatred for Sakura, perhaps as a way to show his growth into a more complex character with a wider range of emotions than just the positive ones shown in the original anime.
Another reason could be that she values the authenticity of the original Naruto narrative. Fanfictions are often the product of fans' wild imaginations and might not align with the official story. She might be a purist when it comes to the Naruto story she is a part of, and thus hates fanfiction that strays too far from the original.
Well, in fanfic, the writer can take creative liberties. It could be that Naruto has grown and evolved in a different way than in the original story. He might have seen Sakura's flaws more clearly over time. For example, her obsession with Sasuke could be seen as a negative trait that affects the team dynamic. And as Naruto values the team highly, this could cause him to develop a dislike and eventually hate for Sakura.
One reason could be for the sake of the Naruhina relationship. To make Hinata seem like a better match for Naruto, the writer might make Naruto hate Sakura. For example, if Sakura is written as being too pushy or bossy in the fanfiction, Naruto could start to dislike her.
It could be that in the fanfiction, Naruto's character is developed in a way that Sakura, within the sasunaru concept, doesn't approve. For instance, if the fanfiction makes Naruto too weak or too different from his original self. Also, if the fanfiction focuses too much on certain relationships that she doesn't like, she would hate it.
In some fanfiction, Sakura might hate Sasuke because of his actions towards her. For example, he may have continuously rejected her advances coldly. This could lead to her developing feelings of hatred as her love is not reciprocated and instead met with indifference or rudeness.
Well, in Naruhina fanfiction, the idea of Naruto hating Sakura can be a device used by writers. It could be due to jealousy in the context of the story, like if Sakura is shown as being too close to someone Naruto doesn't like. Or it could be a misinterpretation on Naruto's part of Sakura's actions. But this is all part of the fictional world of fanfiction, and not a given in the overall Naruto universe.
One possible reason could be for the sake of creating a more complex love triangle in fanfiction. Maybe the writer wants to explore a different dynamic where Naruto and Hinata's relationship is strengthened by having a common dislike for Sakura. It could also be that the fanfiction writer is trying to give Hinata more agency and make her a stronger character by having her oppose Sakura in some way, perhaps in matters related to Naruto's affections.
Maybe Karin has some personal reasons. For example, she might not like Sakura's character in the original work, so she also dislikes fanfic related to Sakura.
Well, it could be that in certain fanfics, the writers want to create a more complex and angsty story. Sasuke's character is often seen as a brooding and driven one. So, they make him hate Sakura perhaps because they think it adds an interesting dynamic. For example, if Sakura is constantly trying to get close to him but he hates her, it can lead to a lot of conflict and emotional turmoil in the story.
Maybe in the fanfic, Itachi has done something that goes against Sakura's beliefs or values. For example, he might have made a decision that put her friends in danger.