I can find literally dozens of examples for you of legally armed citizens forcefully removing a threat, thereby saving the lives of others.
Turban, this particular Psycho probably wouldn't have cared if anyone in that room was armed, but most other violent offenders would. Guns are a very effective deterrent because they remove the advantage from the criminal. The field of force is leveled.
In societies with few guns, it's true that shootings are rare. But violent offenders rarely cease offending just because their preferred weapon gets taken away. I can tell you right now that if it comes down to it, I would MUCH rather be shot than stabbed, clubbed, axed, etc.
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