If the shooter was in fact stopped by an armed citizen what you are saying is 26 dead people is a successful version of your plan.
https://twitter.com/timothycsimons/status/927361223452123136
I doubt that is what he meant. I am pretty sure what he meant was that if not for the armed citizen, there could have been more people murdered.
So, everyone has guns, a shooting event is stopped successfully, only 26 dead!
or, ban some of the damn guns, and maybe have less than 26 dead because they only had a pistol or hunting rifle?