Behavior
Why do we continue to focus on the thing instead of the behavior. Do people actually believe that if the thing was not available then the behavior would not ensue. Be very careful what you wish for. As our militaries and police forces gain an ever increasing technological advantage over the common citizen, it is only a few steps away from tyranny. Our founding fathers were quite aware of the risk of allowing their citizens to keep and bear arms. They also knew that the risk and cost of tyranny was far worse.
If someone in the audience in the Colorado movie theater had been armed and trained I suspect that the casualty list would have been only 1. The perpetrator.