In both the Pittsburgh shooting and the Thousand Oaks shooting, there were “good guys with guns” who tried to stop the shooter and wound up getting shot, themselves.
And then there was the Nashville Waffle House shooting, in which an unarmed customer rushed the shooter and took their gun away.
The strategic genius concludes that having a good strategy is better than having a gun.*
Of course, real experiences are always different. That observation alone ought to silence those who say “good guys with guns” are what you need to stop a mass shooter. But “depending on the situation a good guy with a gun may be a way to stop a mass shooter” just hasn’t got the same assertive ring to it.
* sometimes “good strategy” means “have a gun” – so that covers all the bases.