Some of us think realistically. If I remember right LE responded to that school in 90 seconds. So you have 90 seconds to be a hero and find and kill bad guy and then disarm or you have a real good chance of being shot by LE. Oh and don't forget about the other armed "heroes" who just happen to be looking to shoot some guy carrying a gun.

BTW, the last I checked they don't hire US Army to protect the POTUS, et al. Maybe this is why?