When a person takes one of these weapons and begins indiscriminately killing people it's not an "evil" act, it's the act of a mentally ill individual, plain and simple. When we label it as "evil" we absolve ourselves of our duty to act, because evil is a nameless, faceless, and uncontrollable entity, it's just something we must live with. When in reality what's causing these shooting is the crisis of mental illness that is facing this country, and that is something we can control, but we've chosen to ignore. Mental illness is one of those topics that can't be discussed, it's private, and it's embarrassing, but it's killing us.
Mentally unstable individuals have unlimited access to weapons and ammunition is fully supported by our laws, and by the majority of the population. It's only prudent for schools to hold drills for dealing with active shooters because it's an accepted and encouraged part of our culture.