I could get into a long involved philosophical explanation as to why a belief in God or an afterlife isn’t necessary to prevent us from going around raping and killing each other (via Pandagon), but I won’t – Kant already did it for me.
I’ll just say this instead: what does it say about a person who does hold this idea? Is the only thing that prevents him from murdering his neighbor the fear that he’ll be punished? Perhaps that the only crime is getting caught?
More, it’s the certainty one will get caught. Omniscience, you know. Some beliefs are probably helpful to civilizing naked apes.