Humans used to kill each other all the time. Now it rarely happens (directly), because of a system of crime and punishment. By nature, individuals were sick of being attacked, so they created a system to protect themselves.
That said, you probably meant it is foolish to think you can change human nature from the top-down. Justice may be enforced top-down, but obviously its origins are from the the very grassroots up. Just because you weren't alive when it happened doesn't mean your nature as a person wasn't affected by the justice system, or political system, or that the it was a foolish endeavour.
If you can come up with a system which is so beneficial that even those people who profiting from the status-quo would want to switch to it, then you can change human nature.