If God doesn't exist, how is anything wrong, provided I don't get caught doing it?

I've been thinking about this topic a lot. Since the world is clearly becoming more non religious, why should anyone follow manmade rules on murder and rape and such provided you can get away with it? Isn't it survival of the fittest? Free to take whatever.
If God doesn't exist, how is anything wrong, provided I don't get caught doing it?
Post Opinion