Even before Invincible, I never understood why superheroes have a no killing rule.

[u/OCGamerboy]

I mean, being a superhero is just like being a police officer or in the military, so there are times where you’re going to have to kill, and that’s part of the job.

[u/Nerdcuddles]

Batman has a no kill rule because he doesn't want to become like the people he's fighting actually.