The "Golden Rule" is so simple that more than one pre-Christian culture came up with a version. It's not so much "self-preservation" as "enlightened self interest." Human beings, being social critters, have to get along to survive. The Golden Rule is simply the the distilled-down essence of what it takes to live together.
Now, as for what happens when the other guy doesn't hold to the Golden Rule? Exactly what happens now -- he is dealt with by those around him. God doesn't come down on His magic cloud and smite the fellow. The bad guy's fellow human beings do it.
In the history of mankind, the benefits that religion has brought to society in shaping behavior and moral choice are overwhelming in comparison to the negatives, which anyone can list -- like religious wars and bigotry. Without religion, we'd have anarchy.