He might think it's not in line with the real Steve. Fanfiction can be quite far - fetched sometimes.
One reason could be a difference in ideology. Steve might have very traditional views and Peter's more modern or reckless approach could clash with that, leading to Steve's outburst.
One possible reason could be a misunderstanding. Maybe Steve Rogers made a decision during a mission that Peter Parker thought put civilians in danger. So in a fit of anger, Peter punches him. For example, if Steve chose to sacrifice a small area to save a larger one but Peter had friends in that small area.
Well, one reason could be that he's on a secret mission for S.H.I.E.L.D. that requires him to go undercover and cut off all contact. Maybe he's investigating a new super - villain threat that's too dangerous to let anyone know about.
Well, it might be an exploration of the psychological toll of being a superhero. Peter Parker constantly faces danger, loss, and has to keep his identity a secret. Writers may create 'suicidal peter parker fanfiction' to show how all these factors could potentially break him. Also, in the context of fanfiction, it could be a way to subvert the typical heroic narrative and show a more vulnerable and broken side of the character. However, it's a very heavy and potentially triggering topic.
A possible plotline is that Steve Rogers takes Peter Parker under his wing to train him for a specific mission that only their combined skills can achieve. They have to work through their differences in fighting styles and personalities. Steve might be strict and by - the - book, while Peter is more improvisational. This dynamic could create some interesting conflicts and character growth throughout the story.
One reason could be extreme guilt. Maybe he failed to save someone important and can't bear the burden of that failure. In some fanfictions, if he accidentally caused harm to his loved ones, like Aunt May getting hurt because of his superhero activities, the guilt might be overwhelming.
It could also be a way to subvert the typical superhero narrative. Usually, superheroes are invincible and always triumph. By writing about Peter Parker committing suicide, it challenges the norm and makes readers think about the fragility of even the most iconic characters. It forces the audience to consider the toll that being a hero can take on a person's mental and emotional state.
Some writers might do it for shock value. They want to create a very different and extreme take on the character to get a strong reaction from readers.
Maybe it's due to a new and powerful enemy's attack. In fanfiction, authors might create unique villains with abilities that specifically target Peter's weaknesses. For example, if the villain has the power to disrupt Spider - Man's enhanced senses, it could cause Peter to be disoriented and ultimately collapse. Another aspect could be that Peter overuses his powers without proper rest, which exhausts his body and causes him to collapse.
Perhaps Steve in the fanfiction was involved in a cover - up of some sort that affected Peter. Say, Steve knew about a threat coming towards Peter but didn't tell him in time because he thought Peter couldn't handle it. When Peter found out, he felt betrayed and thus couldn't forgive Steve. Also, if Steve accidentally caused harm to one of Peter's friends or allies while on a mission, that could be a major factor in Peter's unforgiveness.