in all of these shootings I think, "if only they had been packing heat".
If more people carried sidearms there would be more of these murderers cut down?
There are some studies which say "yes".
"Gun free" zones likely the worst. The perp knows nobody else is armed and can be easy targets with no retaliation.
Better the bad guy being concerned "somebody/everybody is armed and I'll likely get killed" if I go shooting the place up.