You do. That's what concealed carry is all about. I've read a lot of comments on this site, but truth be told, the killer in a situation like this only stops when they run out of ammo, the firearm jams, they decide to commit suicide, they sit down and quit, or they are killed by someone else, often times by a responding individual with a gun.
No LE, or concealed carry, or legislation, is effective in stopping all crime, and/or murders. But for me, having been part of a sweep team in a public school, trained to sweep the hallways in the event of an active shooter in the building, I'd rather be armed in that situation, than not.
Armed intruder in the building. All classrooms doors to be locked. Some kids possibly stuck in hallways, bathrooms, etc. Sweep teams designated to sweep through the building, rounding up students, getting them out of harms way if possible. We even had local LE participate in trainings.
One thing I read on here, indeed, confusion can arise as to who's who. Upon sight of LE, sweep team members were trained to hit the floor flat out with hands on head so LE knew. We all had radios, and other details too numerous to mention.
I can assure you it was a detail that none of us cherished.