If this is supposed to make me feel sorry for Mon....I don't.
Let's say that at one point in time he was devoid of reasoning of right and wrong, and didn't fully comprehend the weight of his actions.
He later learned to empathize with the pain of others after his first run in with the monster and still chose to kill, to affirm himself.
And he had enough sense to tell Toshi not to kill Maria because he understood the value of her life to him, so he definetly could understand that other lives held value as well.
Initially I viewed him as a child or having the understanding of one, much like he was portrayed here, but he has been shown to have the capacity to learn throughout his journey.
