That's one point. But a kid with a concealed pistol could walk by and shoot AR security man in back of the head. Sounds ugly, but if someone is really intent, taking out a uniformed guard/cop would be easy. Plain clothes has it's drawbacks in this application as well because they'll be immediately seen as a teacher/authority and can be shot from 50+ yards distance. No easy answers for those really intent.
Gotta keep em guessing
I’d rather die with a gun in my hand trying to protect someone...than not.