Well, if such a fanfiction exists, it's really disturbing. It goes against the positive relationship we expect between Sirius and Harry in the original Potter universe. It might make many fans uncomfortable as Sirius is often seen as a protector figure for Harry.
One way is for the fanfiction platforms to have strict content guidelines. They can ban such disturbing content that goes against the positive nature of the characters' relationship.
It is not okay. Fanfiction often expands on the existing world and characters, but when it involves abuse like this, it can have a negative impact on how readers perceive the characters. Snape had his difficult relationship with Harry in the original series, but 'abuse' is a very extreme and inappropriate way to represent that relationship in fanfiction.
It's not a common statement at all. Fanfiction is a creative and collaborative space. Normally, people are respectful towards it. There would have to be a very unusual situation where someone named Harry was doing something really wrong with fanfiction for such a statement to be common. Maybe if Harry was constantly stealing ideas from fanfiction and passing them off as his own in a big and public way, but that's not the norm.
It could mean that a character named Harry is misusing or treating fanfiction in an improper way. For example, if Harry is a writer, he might be plagiarizing elements from fanfiction, or perhaps he is using fanfiction in a way that violates the ethical or legal norms of the fanfiction community. However, without more context, it's hard to be certain.
One reason could be Harry's impulsiveness. Harry often jumps into dangerous situations without thinking, and Sirius, being his godfather and having a protective nature, would shout at him to make him realize the risks. For instance, if Harry decides to go after a Death Eater alone.
Well, often there's a theme of internal conflict. Draco may be in a situation where he's been taught certain values in his family that lead him to abuse Harry, but deep down he might be struggling with his own conscience. And also, it can show the impact on Harry. Harry, being the victim, could be depicted as becoming more resilient or, on the other hand, more withdrawn. But really, this is a rather dark take on the characters compared to how they are in the official books.
The ethical problem also lies in the potential harm it can cause to the fans who love the original characters. Fans may be attached to the positive relationships in the original series, and seeing a character they love being involved in an abusive situation in fanfiction can be emotionally distressing.
Fanfiction should be a place for creativity and positive interpretations. If there are stories where 'ron abuses harry', it goes against the spirit of the original series. The 'Harry Potter' series is about friendship, and any fanfiction that involves abuse is not in line with that. We should focus on fanfictions that build on the positive aspects of the story, like their adventures and growth.
Well, it could be considered an ethical problem in terms of the impact on the fanbase. Younger fans who are used to the positive and heroic stories in the 'Harry Potter' world might be exposed to this rather dark and inappropriate fanfiction. This can affect their perception of the story and the characters. Moreover, it might violate the general spirit of the original work which promotes love, friendship, and heroism.