Men have no better angels. When their faith and fear of God vanishes, it creates a terrible vaccuum into which the most horrible things imaginable rush in. The psychopath could never recognize God - as Nietszche pointed out, who needs the competition? God is just another male in the way of what they want.
It doesn't matter if God exists or doesn't exist. You're not a good atheist until you realize this. Men have no better angels. Only fools and idiots speak of principles without divine sanction. The king monkey will just throw those principles out if they represent restraint and replace them with values that permit them to act however they wish.
As soon as the Bolshevists came to power in Russia, they set out to eliminate the intelligentsia first. The men who had written of a perfect managed State based on altruism were the first to kneel at the edge of mass graves.
Every useful tool in history has advocated a nation without a God and almost none of them were allowed to live long enough to see what a nation without God looks like.
Man is not a learning animal. Man has no better angels. If you don't know these things yet, you're either young or stupid. If you're young, there's a chance you will understand these things someday. If you're stupid, you would not understand anything if you lived a thousand years.