A world in which human nature was allowed to go unchecked by a social contract would be a dismal world. This world would likely resemble that which Hobbes describes where life is “nasty, brutish, and short.”
Human nature is not all bad, but it certainly has very bad elements in it. We human beings are clearly inclined to be greedy, selfish, and violent. If we did not have social contracts that rein in these inclinations, we would tend to act on them. We would have a society in which many people (if not all) would take as much as they could get, even if that meant committing violence against other people.
Therefore, we need social contracts. Usually, this means that we need a strong government that can punish people who break the social contract. Less frequently, it can mean that we need extremely strong social sanctions against deviance (Japan might be an instance of this) in which social expectations, more than anything, deter people from committing crimes. One way or another, though, it is necessary to have some sort of social contract that is enforced strongly. If we do not have such a thing, our society will descend into chaos and anarchy.