One possible reason could be a misunderstanding. Maybe some dark magic was involved that made Harry believe the Weasleys were acting against him or the wizarding world in a way that seemed illegal. For example, if there was a spell that distorted his perception of their actions.
Well, it would surely strain Harry's relationship with Hermione and Ron. Ron would be extremely angry and hurt that his best friend got his family arrested. Hermione would probably be disappointed in Harry and try to figure out what went wrong. Their friendship would be in jeopardy.
Maybe Harry accidentally frames Weasley for something. It could be due to a misunderstanding, like a spell gone wrong that makes it seem like Weasley was involved in some illegal magic use.
Maybe it's a corrupt Ministry of Magic official. They might use Harry's credibility to their advantage and trick him into providing false information about Weasley. They could be after the Weasley family for political reasons or because they want to cover up their own misdeeds by creating a distraction with Weasley's arrest.
Dumbledore would be a key figure in the reactions. If he believed in Snape's innocence, he would try to find a way to free Snape while also not alienating Harry. He might start his own investigation to uncover the truth. The other Hogwarts teachers would be in shock. Some might believe Harry is right, especially those who have always been a bit suspicious of Snape, while others would be outraged and demand an explanation from Harry.
Maybe in that fanfic, there are misunderstandings between Harry and the Weasleys. For example, they might have had an argument over something like magic use or family values that led Harry to dislike them.
It depends on the nature of the touch. If it was an innocent accidental touch, then the arrest might seem extreme. However, if it was inappropriate or non - consensual, then the arrest could be seen as a necessary step to protect the girl. There should be a thorough investigation to determine the true intentions behind the touch.
Perhaps it was because of the power he amassed in the process of defeating Voldemort. In the fanfic world, power can be a very scary thing to those in authority. Harry's new - found and possibly overwhelming power could have made the existing magical power structure feel threatened. So, they arrested him as a way to control and contain that power, rather than seeing him as a hero who saved the wizarding world.
The Weasleys are likely to be horrified. They are a warm - hearted family. Mrs. Weasley might immediately take on a motherly role towards Harry, perhaps making him his favorite foods and fussing over him. Mr. Weasley could become very protective, ensuring that Harry is safe from any further harm. The siblings, like Ron, might be angry that Harry had to endure such abuse and vow to always have his back.
They might be shocked and sympathetic. The Weasleys are a kind - hearted family. When they see Harry's scars, which are symbols of his difficult past, they would likely show concern. For example, Mrs. Weasley might immediately fuss over him, asking how he got them and if they still pain him.