Aside from the fact that there have been “civilians” who have stopped shooters, there is one other point to consider.
Schultz and his ilk have prevented it from happening more often by establishing their “gun free zones” which most gun owners (being a respectful lot, by and large) abide by.
"Gun Free Zone" signs should already be at the recyclers.
ADT or other security services should be the norm... With signage all around the facilities in plain view.
With cameras all around the campus, I bet child sex abuse goes down, too.
When we had a new priest come to our Church, he immediately replaced wood doors with glass doors in the offices. No one could ever accuse him, or any of the staff, of any hijinks because they were visible through the glass.
Cameras all around the Church were installed - for reasons set up above and for stopping thieves.
I think the insurance policy assigned credits for taking these actions, so the policy cost went down. Win-win. "An armed society is a polite society." (don't have attribution, sorry)