Would You Obey?

In Law class we are learning about the different theories of law. Where did law and fairness come from? I guess I'm a Naturalist when it comes to the origins of law. I think we all have something deep inside of us that someone "knows" when something is not fair or right. I see it in kids all the time! "That's not fair!" We know we're getting jipped when our sibling gets a larger piece of cake than us, and we know its not fair when we get the bigger piece too. We know something is not right when we see people killing each other. We know something doesn't feel right when someone takes "our" stuff. But why? Would we refrain from stealing, killing, speeding, etc for the sheer reason that we knew it was good for the common man, or do we think there's something in it for us? Do we assume that if we don't do wrong, wrong won't be done unto us? I wonder how the world would be different if we had no laws or rules. I think the world would be bad, but not because there would be more people doing bad in the world. I think the bad people in the world would just being doing more bad things, worse bad things than they already do. I think, in general, maybe naively, that the majority of people in the world would still do "right" simply because they think its "right". They wouldn't steal or cheat or speed. They just wouldn't. There would not be a need to. But maybe I'm wrong?