Nobody here mentioned the death penalty. However, a person with a CCW legally stopping a criminal helps to ease the issues you speak of. The person is stopped while in the middle of their crime. They are now unable to do more harm than they already have. No need for a trial, money saved. No need for space in a prison, money saved. No need to go through the appeals process, time and money saved. No need to go through the execution, money saved.
WIN WIN WIN
Badguys lose
If just one person in that classroom had a CCW, was allowed to carry in class, and had some halfway decent training, then less people would have been shot. FACT.