Board Thread:Questions and Answers/@comment-61.6.238.10-20161107022633/@comment-27001684-20161107160121

Simple, he isn't someone who kills humans on purpose. He isn't a murderer, he's a hero after all (The exception being EVIL monsters, who are inhuman).

If you were a hero, would you kill humans? A hero protects humanity, just stopping evil humans is enough. Saitama himself is a human after all.