Security has a place. But even at schools, really all it can do is prevent a handful of deaths from turning into dozens or hundreds. You can have someone manning a metal detector at the front door. But a gunman can just walk in, shoot that person first, and walk right through the security checkpoint. Lockdowns and secure classrooms help, but they can still shoot plenty of people as they’re running for the exits or running to the secure classrooms. If a gunman comes to a high school during their passing period, there really just isn’t anything that can be done to prevent them from taking a handful of lives at a minimum. Even having armed swat teams available within minutes just reduces the final body count; it doesn’t eliminate it. When you can just walk into a crowded building and start spraying gunfire, security really just can’t prevent that, just ameliorate it.