With no punishment expected in the after life, the only thing that keeps people from behaving in a bad way would be a fear of being caught and punished, in the present. With no silent watcher seeing everything a person does, there would be no reason to comply with any laws a society might make. If I kill you, so, if I don't get caught, what is the big deal. To you, yeah, and your family, but to me, if I got what I wanted from the killing and didn't get caught that would be the end of it. As humans show time and again, compassion is something that has to be taught, at least to most of the people in the world. Look at any play ground, it isn't exactly a paradise of peace and understanding, the adults, who have been taught through a long history of religously based ethical codes, step in to correct the behavior.