Don't know if you considered it, but being ARMED has a LOT uses in a chaotic mass shooting.. Instead of playing RAMBO -- you can do like MOST of the armed police do and SAVE lives that you can.. Having a gun with you makes you more likely to be able to defend those you're trying to rescue...
You have a very simplistic view of what the value is to be armed.. Providing safety to a group by being armed is what most officers on scene are doing. Very few have the opportunity to "take the perp down"....
The greatest safety is provided by deterring shooters from coming, by having armed people present. This is a red light to the shooters.
By taking away this deterrent, the shooters get a green light, and clear invitation to come in and shoot up the place. This is where shootings occur, In gun-free zones where shooters are like electricity following the path of least resistance.
Yes it is quite simple indeed. No need to make anything more complex out of it.
So you got an answer to the title of the thread ? If so, let's hear it.