Why does Harry refuse to listen to Dumbledore in the fanfic?

Maybe he has his own reasons. He might be tired of the responsibilities that come with being a hero. In the fanfic, perhaps he has seen the dark side of heroism, like the constant danger and the loss of personal freedom. He could also be a complex character who doesn't conform to the typical heroic image.

There could be ethical reasons. Fanfic sometimes involves using characters and settings created by others without proper authorization in a more complex way than just being inspired. Harry might not want to get involved in teaching something that has such potential legal and ethical gray areas.

Maybe he has his own personal reasons. He could be afraid of failure, or perhaps he doesn't like the competitive environment. Another possibility is that he has some moral objections to the nature of the competition in the fanfic.

In some fanfics, Harry might hate Dumbledore because he feels Dumbledore has been using him all along as a tool to defeat Voldemort. Dumbledore has been making decisions for Harry without fully considering Harry's feelings and desires. For example, he didn't tell Harry about the prophecy until it was almost too late, and Harry might see this as a form of manipulation.

Maybe in the fanfic, Harry has some unresolved personal issues. He could be haunted by his past traumas, like the death of his parents and his battles with Voldemort, which make him feel that he's not in the right mental state to get married.

Maybe he has his own principles. In some fanfics, Harry might have a different view of SHIELD's methods or goals. He could be more of a lone wolf type and doesn't want to be part of a large organization like SHIELD.

Maybe Harry has a major disagreement with Dumbledore's decisions or strategies and thinks a duel is the only way to settle it.

He might think fanfic distorts the original concept.

Maybe he has a very traditional view on literature. He might prefer to stick to the original works and not engage with the fan - created versions. Fanfiction often takes the original story in different directions which he may not like.

One possible consequence is that Harry could put himself in danger. Dumbledore is usually very wise, and his advice is often meant to protect Harry. By not listening, Harry may walk into a trap or face a more difficult situation than he expected.