No, not really. These series are based on light novels, which often are based on web novels, basically self-publications, meaning, there's no limit to them. I reckon in Japan, with it's society constructed to be highly competitive yet uniform at the same time, there's strong demand for edgelord and revenge fantasies. After all, traditionally in Japan a bullied person isn't helped by the society, instead the bullying victim is blamed for getting bullied and told to deal with it. Bullying isn't traumatic only for the targets but also for some of the onlookers if they happen to be empathetic people or if they fear they will be the next victims. It's not hard to see how there's a continuous stream of new customers for revenge fantasies.
How exactly is it silly? The oldest form of justice in the world was revenge, either by the victim or by their relatives. In fact it's still so in some unfortunate parts of the world. In most of the world the revenge was simply institutionalised. However, in lots of cases it still depends on the victim, or the victim's family, to report the offense and/or sue the offender.
World celebrates him? Where exactly did you get that from? Dude's automatically a fugitive. Why did you think he waited until the king is away, prepared a double by mutating the knight, and then sneaked out, altering his own looks and name (though the alias is as stupid as in these stories normally). He's on the run. The whole kingdom is basically his enemy right now. Just like if you killed a person who had assaulted you previously, you'd be hunted by the law enforcement of your country. This dude attacked the very government of the country.
I don't know why you are calling this porn, though. Sex, so far, has been nothing but acts of violence in the story. Furthermore, you could remove those scenes, wholly or partially, and little would change. With real porn, you would have the customer calling you angrily and demanding their money back if you removed sex scenes. This is an edgelord revenge fantasy. Rape is a part of it, just like maiming and killing.