It is said, those who fail to learn from history are bound to repeat it. With each mass murder, we should be seeking to learn what we could have done to avoid it.
I do not know whether any of the mass murders has left a more clear solution than the Bastille Day massacre, where the truck plowed down so many people. A day or two later, I heard a news commentator speaking of how barrier (usually made of concrete) prevent vehicles from jumping into areas filled with pedestrians.
What I want to know is, why haven't we seen a big call to build these barriers along our busiest sidewalks, and along our parks? Why? Those who fail to learn from the present will be stuck in it. If you would have a future you must learn from the present. If we do not learn from the mass murders happening now, we will not begin to escape them. It seems, each time when you see a way to lessen the ways a mass murderer can achieve his objective, you snap to reduce what he can do.
There will still be many ways for the killer to achieve his objective, but we will have taken one tool out of his hands. And, though you cannot make a count of crimes that never materialize, this will prevent a slaughtering somewhere along the line.
Those who fail to learn from history, fail. And, we will fail, if we do not pause to look for an answer each time there is a slaughtering. Those who will not take their lessons from the present, must again be administered them in the future. We must adapt or die.