Well, several hundred years ago several philosophers and political theorists including Thomas Hobbes and John Locke and Jean-Jacques Rousseau put a name to this sort of thinking - the "social contract". Basically this theory goes something like this... everyone gives up certain autonomy to a governing body so as to maintain social order. In my little running scenario that means the drivers on the street acknowledge that a governing body has set up the sidewalk as a safe haven for walkers, that driving on the sidewalks is dangerous and therefore against the law... so they don't do it.
Of course, most people don't even think like this. Hitting a sidewalk is terrible for your car, and people in general don't want to hurt those on the sidewalk, or in any case most people are just too busy to care and they are trying to get from Point A to Point B as quickly as possible. You and I don't think about things like social contracts... we just don't want to ruin our day. But when someone does do something like that... like running up on a sidewalk to take out unsuspecting runners... we think it's tragic, and in a sense we become a little more fearful because someone has broken the unspoken agreement.
CS Lewis took this a step further... he said that sense of right and wrong... that sense of a "social contract"... really originated with God himself. In Mere Christianity, he states that every person (meaning those in their 'right mind') has an instinct to abide by what he calls the "moral law". And this instinct cannot be explained apart from God. For if we try to argue that people do good for their own good, then we might look at people who steal from others and get away with it and say they did bad for their own good... But if the moral law is for a person's own good then even the theft might be considered good... so that fails. Well, then what about doing good for the good of society... well there again we might question, which society? Lewis cited Hilter and the Nazis and the abomination of the Holocaust... in their society at that time they believed they were doing what was good for their society. But no one (in their right mind) would say the Holocaust was anything less than one of the most evil acts perpetrated on humanity. So again, the argument that morality is defined by society fails...
There are many other arguments about the origin of the moral law (or the lack of any moral law), or what causes people to act according to generally the same rules, but ultimately there has to be something outside humanity that determines the rightness and wrongness of things... for we all at some point say, "That is wrong" or "That is right." There has to be something that determines that statement outside of ourselves, because relativistic arguments just don't hold up.
Paul, writing to the Romans explains our confusion with right and wrong pretty well I think... (this is The Message paraphrase)
The basic reality of God is plain enough. Open your eyes and there it is! By taking a long and thoughtful look at what God has created, people have always been able to see what their eyes as such can't see: eternal power, for instance, and the mystery of his divine being. So nobody has a good excuse. What happened was this: People knew God perfectly well, but when they didn't treat him like God, refusing to worship him, they trivialized themselves into silliness and confusion so that there was neither sense nor direction left in their lives. They pretended to know it all, but were illiterate regarding life. They traded the glory of God who holds the whole world in his hands for cheap figurines you can buy at any roadside stand. Romans 1:19-23
We often don't acknowledge that God has revealed all this to us, we don't give him the credit he is due, and Paul says, we act as though God's input on things like right and wrong don't matter... we trivialize him and so we trivialize right and wrong itself.
The question is where will it end up? When we, who are imperfect, think we can define the standard for right and wrong... where will we end up? Just exactly where we are... People want to know why we can't get a handle on the state of our world, I think it's because we continue to refuse to acknowledge God as God... and that his is the ultimate standard.
