But ultimately, his obsession with dealing out due punishment ( or worse) and his refusal to think about what he's doing twists him into a monster just as bad as, or even worse than, the one he's hunting. Other characters within the work itself might even concede that point.

Our avenger may have good intentions he might have a point when he says that the fiend is too dangerous to be kept alive. Unfortunately, we can also see that the more he hunts the cause of his woes, the more he takes on the villain's personality and mannerisms - something that our so-called hero is too blinded by his single-minded goal to realize. He may justify his actions by claiming that it's justice he's after, not vengeance, but anyone with half a brain can easily see that he's out for revenge. All that matters is that It's Personal, and he feels that the law just isn't suitable enough (or has become too corrupt and ignorant) to be of any use to him in settling the matter. Something has happened to our Fallen Hero: his village was destroyed, his friends were killed, his puppy was roasted on an open spit, his bike was stolen, whatever.

He Who Fights Monsters is not quite a villain, but they act antagonistically enough that they're little better than a villain. will become no better than the monsters he slays. Friedrich Nietzsche, Beyond Good and Evil

Out of the abyss tracking survival