How about laws against murder and slander (false witness)? What is your point?
So you choose some sins to legislate against but not others? Why do you pick certain sins but not others if you think the laws are there to protect morality?
I'd add theft as well. But what about worshipping other gods? What about taking the Lord's name in vain? These are big-time sins according to the Bible, why shouldn't they be enforced by the state?