I could rest my case with your statement "It hasn't happened yet" in combination with the fact that multiple independent studies have shown that there are over 2 Million cases of self defense uses of a gun by average citizens every year in the US alone, 98% of the time without even needing to fire a shot, that in combination with the fact that roughly 2-3% of the citizens in most of the shall issue CCW states already have CCW permits & carry every but gun free zones. If it hasn't happened yet, odds are good that it won't happen often if it ever does, and adding one more location where CCW permit holders can carry isn't likely to change that. As for your question on why someone bent on shooting lots of disarmed defenseless victims with plans to shoot him or herself before the Police can confront them would be willing to put down their gun in the face of someone else aiming their gun at them, I'm not sure why they do. Perhaps it is before they're ready to die, perhaps they want to prepare themselves mentally to kill themselves. Perhaps it is because the thought of being shot by someone else before they are ready throws them off their game long enough to cause confusion. I do know that in both of those cases I mentioned the shooters had planned to off themselves & in both cases they put down their gun when confronted by an armed citizen commanding them to do so. Even if not, better for there to be a shootout between an armed citizen & the shooter than for the shooter to be able to continue his or her killing spree knocking off person after person with nobody around to attempt to stop it.