Sigh.... Focusing on revenge and disregarding the consequences of his revenge towards the entire world and the people he cares about. What a petty guy. And you support such actions? Pathetic. You know what? People like you are the real reason why WW and big conflicts irl happens these days. The real reason why there's never peace.
Dude you realize this manga is all about revenge from chapter 1 right? And the theme itself is about revenge. What do you want people to talk about? food?
Every action have consequences. letting the bad guys live have consequences. Even doing nothing have consequences.
Let them live will have the consequences of them having a grudge on MC and can make the MC the bad guy from their side. What can they do to get revenge on the MC? Massacre another hundreds of people as an offering to bring another "hero" From the other world.
You always preach about justice. But justice Itself is a matter of personal opinion. What you consider justice is not always what the other people consider justice. Even your enemy have their own version of justice.
That's why the word "JUSTICE" Always used in every different religion, politics and such even though their value is different from each other. Different religion have different value of justice and sometimes clash with each other.
You might see it as forgiving the bad guy as a "justice". But from the stand point of someone that suffering and losing the loved one because of them, killing them is justice. That's why Justice is a gray word without clear side of black and white.
If you want peace in this world. Justice is not what you should seek for. It's Compassion