Well, some fanfic writers might explore such a concept for the sake of creating an alternative storyline. Maybe they want to see how the dynamic between Harry and Hermione would change if there was conflict or hatred, adding a new and unexpected twist to the well - known relationship.
One possible plot could be that Hermione does something that Harry perceives as a great betrayal, like perhaps siding with the Ministry when Harry believes they are corrupt. This could lead to a deep - seated hatred from Harry.
Perhaps in the fanfic, there is a love triangle situation involving Ron. If Harry unknowingly gets in the way of Hermione's relationship with Ron, she could develop hatred towards him. Another aspect could be that Hermione feels Harry is getting all the credit for their group's achievements, while she is doing a lot of the behind - the - scenes work, which makes her resentful.
There may be some fanfics out there with this premise, but it goes against the general relationship dynamics in the official 'Harry Potter' universe. Usually, Harry respects and values Hermione. If such a fanfic exists, it might be written by someone who wants to explore a really dark or different side of the story, like if there was a major event that made Harry turn against Hermione in that fictional narrative. But I haven't actually come across one myself.
One possible reason could be a miscommunication. Maybe Hermione accidentally reveals a secret of Harry's that he didn't want known, and this causes him to feel betrayed and start to hate her. Another reason could be jealousy. If Hermione gets more attention or praise for her magical abilities than Harry in the fanfic, he might develop feelings of envy and hatred. Or perhaps there's a love triangle situation where Hermione is involved with someone Harry doesn't like, and that causes his hatred.
Yes, there probably is some amount of it. However, in the official books, Hermione and Harry have a very strong bond. They support each other through countless challenges. Fanfiction like this may explore alternative character dynamics, but it's not the mainstream view of their relationship.
Perhaps in this fanfic, the Weasleys have some actions that conflict with Harry and Hermione's values. For example, if the Weasleys were to make a deal with a dark wizard for the sake of their family's safety and Harry and Hermione found out. This could lead to a rift and hatred. Also, it could be related to a love triangle situation in a very convoluted way. Maybe one of the Weasleys unknowingly gets in the way of Harry and Hermione's relationship, or vice versa, which causes animosity.
In the original story, Harry and the Weasleys are like family, and Hermione is also very close to them. So in the fanfic, the hatred is a huge deviation. It goes against the established relationships of friendship and family that are central to the original plot.
Some writers might create such fanfiction for the shock value. They want to break the established strong friendship in the original series to get readers' attention.