Even if the police were functioning well enough to act to stop a school shooter, there is still the issue of time — it takes time to arrive to the scene to respond to the threat. A competent on-site security presence would be a good first line of defense. Think of a time sensitive scenario like a home invasion — would you rather have the means to immediately protect your home, or would you rather wait for the police to arrive? What if someone attacks you on the street? Would you rather have the means to immediately protect yourself, or would you rather wait for police to arrive? In some cases, no matter how competent the law enforcement is, it’s simply impossible for them to respond fast enough.