One possible reason could be that Snape has his own unique way of teaching discipline. He might believe that a more forceful approach like spanking would make Harry more cautious in his actions. Maybe he thinks Harry has been too reckless and this is his extreme method to instill a sense of responsibility.
It could also be that Snape has some unresolved issues from his own past. He might be projecting his own experiences onto Harry. Maybe he was once in a similar situation and wishes he had someone to correct him in such a harsh way, so he believes it will be beneficial for Harry.
Perhaps Snape is trying to protect Harry from greater harm in the long run. By spanking him for his mistakes, he aims to make Harry realize the seriousness of certain situations quickly. In the wizarding world, there could be dangerous consequences for Harry's actions, and Snape wants to prevent those by being strict.
One possible reason could be to protect Harry. Snape might believe that by tying Harry to the bed, he can keep him in a safe place away from immediate danger. Maybe there's a threat in Hogwarts or outside, and Snape thinks this extreme measure is necessary to ensure Harry's safety.
Harry is likely to be angry at first. He has always had a tense relationship with Snape, and this act of spanking would seem unjust and humiliating to him.
Maybe Snape has some sort of premonition or knowledge that Harry is going to be crucial in the fight against dark forces in the future. So, in order to ensure that future, he steps in to save Harry from whatever danger his parents' situation might put him in. He might also be trying to atone for past mistakes or grudges he held against Harry's father by protecting his son.
Maybe Snape suspects Harry of being involved in some sort of dangerous activity related to the Dark Arts. Pressing him to the wall could be a way to force Harry to come clean about his actions or any knowledge he might have. It could also be that Snape is acting out of his own insecurities and pent - up emotions towards Harry, which he has been suppressing for a long time.
One possible reason could be Snape's long - held grudges and resentments. He had a complex past with Harry's father, James Potter. Snape might see too much of James in Harry and be unable to separate the two in his mind, leading to his rejection.
In fanfiction, his wand could potentially be used to reveal secrets. Snape was full of secrets himself. Maybe his wand could be a key to unlocking hidden chambers or revealing long - lost knowledge. It could be used to decrypt old spells or manuscripts that were crucial to the wizarding world's history.
One possible reason could be that Snape is still holding a grudge against James Potter, Harry's father. He might take out his long - standing anger on Harry. Another reason could be that Snape is trying to discipline Harry in his own strict way, but it ends up being too harsh and making Harry cry.
One possible reason could be Snape's long - held grudges and resentments. He has a complex history with Harry's father, James Potter. Snape might see too much of James in Harry and be unable to separate the two, thus rejecting Harry despite any potential father - son connection. Another reason could be Snape's own self - loathing and his belief that he is not worthy or fit to be a father figure. He may think that he would only bring harm or a bad influence to Harry's life.
One possible reason could be that Snape is trying to intimidate Harry. He has always had a rather tense relationship with Harry in the original story, and this could be an extreme form of showing his authority. Maybe he suspects Harry of something, like being involved in some mischief or having knowledge about a certain Dark Arts item or activity.
One possible reason could be punishment. Snape has always had a rather thorny relationship with Harry in the original series. He might see this as a way to assert his authority over Harry. Maybe Harry has done something in the context of the fanfiction, like accidentally messing up Snape's potion ingredients or getting into an area of Snape's house where he wasn't supposed to be.