It strikes me as inherently unproductive, on a societal level, to make vengeance a policy, as it so often results in a positive feedback loop of grievances. The grievances of the punished are not recognized as legitimate, so they're frequently displaced onto others, creating more desire for punishment and eventually more victims.

Admittedly, you're expressing a common sentiment. I've never been the victim of a violent crime, so I can't speak to the experience of feeling a need for satisfactory vengeance. But it seems to me to be one of the worse aspects of human nature, which we should seek to overcome through enacting laws seeking restorative justice, or at least non-vengeance based punishment systems. Unfortunately, the letter of the law has little to say about the underlying human desire for vengeance when wronged, and instead seems to often start from the axiom that satisfaction must be given. I wish this were more frequently and publicly questioned.

FYI, this is an excellent book on the subject: "Inferno: An Anatomy of American Justice" by Robert Ferguson (http://www.hup.harvard.edu/catalog.php?isbn=9780674728684)