Why obey a God you can't see?
As an Atheist I actually do obey some of the biblical laws. I haven't killed anybody and I'm not a thief but I refrain from those things not because of some vague afterlife punishment but because I don't want to hurt anybody.
God doesn't want us to have s** outside marriage but that injunction I do disobey. I have no fear of an after life punishment I merely don't want to steal something or hurt anybody.
You don't need a God or a religion to treat people right.