Something in a manga that is very sane and normal but pokes you the wrong way?

I'm going to sound stupid when I say this but yk,the mangas with murderers or where the killers kill is justified because they're killing assholes or 'cleaning up human filth'. Idk doesn't set right to me lol. I can't justify taking law to your hand and killing someone even though they are 'human filths'...it feels like i'm nagging lol but it really pisses me off when killing is being tried to be justified anywhere or anyhow.