Good point. Their societies, while officially atheist, amounted pretty much to religions. But atheism, per se, is not sufficient. There are things about humans that are good and things about them that are not so good. And there will always be people around who will try to take advantage in whatever way they can manage.

If everyone on the earth were an atheist, tomorrow there would be some other stupid reason to kill each other. If everyone on this earth were chinese, the next day we'd find some other reason to find fault.