Yes, and the only way to mitigate it is to eliminate killing fields, er, 'gun-free zones' , stop glorifying these nutjobs, and start glorifying those individuals who stop them, particularly when it isn't in their job description.
When I was in ROTC many years ago, I was taught how to respond to an ambush. Attack with speed and violence of action, because it is the only possible way to get out of it alive. Sadly, the company i work for has a strategy that is passive in nature, until the very last second. (ADD, Avoid, Deny, Defend, used by many businesses) I will be fired if in such a situation, if I am not killed, because the training will take over; to me ADD means Attack, Defeat, Destroy.
Perhaps such training as I received in ROTC should be taught, maybe 5:15 to Paris should be shown in schools as an example of how to react. It won't turn all the kids into would-be John Waynes, but it just might tip the balance enough so that the next 'big tragedy' becomes a blip on the radar, with the perp captured or dead, and a kid who's reaction was 'I was dead for sure if I hadn't rushed him...'