Ok, let me take another crack at this morality thing.
All actions have consequences. Actions which have negative consequences are, in most respects, "incorrect." For example, touching a stove has the negative consequence of burning your finger, making this action incorrect. Actions with negative consequences to self are considered stupid, unless they bring postivie consequences to others, such as sacrificing life, limb, etc. to save the lives of others. Actions which have negative consequences to others are immoral. Now, understand that there is a larger scope involved. Some people would say that suicide and drug use are not immoral, since they only harm yourself, but drug use brings negative consequences to all who depend on you for anything and suicide brings negative consequences to those who care about you. This is pretty much a universal definition of morality.
Now, you can debate many ideas of what is harmful and what is not all day long, but this is what it boils down to. You believe one of two ways.
1) Secular: Ancient man began to abide by and enforce these rules as an evolutionary societal step. When not everyone followed these laws, man took their idea of a divine being which controlled the sun, the weather, and other things they didn't comprehend, and they expanded that idea to include that this divine being would punish those who were not punished in life and reward those who adhered to the rules. In this way, laws led to religion which led back to laws.
2) Religious: A divine, all-knowing being told ancient man practices which were not good for them as a whole, forming religous law. People enforced these laws, but for those who weren't caught, they were assured that God would punish them in the afterlife if they didn't make some sort of amends. Eventually, society decided not to intertwine religion with law, so they seperated out which laws should be enforced by the state and which ones should be left to the church. Other societies broke away from religion completely and entirely dumped the laws that they didn't understand.
Either way, modern laws stem from religion. Where that religion stems from is the subject of debate.