It's like: "We'll kill the killers the right way ('humanely', with due process, etc.) so you don't go vigilante and murder them yourselves." From this angle, a

It's like: "We'll kill the killers the right way ('humanely', with due process, etc.) so you don't go vigilante and murder them yourselves." From this angle, assuming no other considerations, the legitimacy of the court system hinges on how often we see revenge killings. One could argue that the U.S. is more civilized now, so discouraging revenge killing is a fairly minor consideration.