Sometimes you hear ant gunners claim that concealed carry or armed security is not an answer, that it might not work against a mass shooter. I remembered something that my father (co pilot) once told me about his WW2 experiences that might be relevant, an analogy I guess. One day he had a non army passenger on his plane, and the passenger was told they might have to abandon the plane in an emergency, and what the emergency procedures were. An emergency landing was simply not possible due to the terrain below. You stay in the plane you die, simple as that. The guy had never jumped before, and asked if they could ensure that the parachute would open properly and that he would land safely. The pilot replied, "Ensure? no. But you're always free to jump without one and take your chances."