Crime, Certainty, Immediacy

In terms of crime deterrent from a state point of view, this is brilliant.
I have been saying, to friends and family, for a long time that immediacy and certainty matter a lot more than the severity of the punishment. From a non-state view, this sugests that violent crime would go down if more people were willing to use force to protect their fellow man.

Also, from this we can conclude that if people fought back against muggers, rapists, thieves, etc, we would see a lot less of that sort of crime.