Other venues than schools have since become the scene of mass shootings, though it remains the favored locale for the young shooter. Mental illness is a common theme, whether or not identified. There is a kind of narcissism involved, in which other people are merely props for one's own personal Götterdämmerung. And still, people ask Why.
There is a dreary sameness to these events, wherever they occur. They've become a meme, a trope. There's a beaten path, a "right" way to go about committing such an atrocity. It is less about specific grievances (real or imagined) and more about . . . who knows? I am reminded of something that a friend of mine said. He had a Ph.D. in Anthropology, had studied Melanesian society and others, then felt a call to ordained ministry. After pastoring for a few years, he became a Missions professor at the seminary we both went to. He said to me once, "Every society has a socially acceptable way to go crazy."
That means that persons suffering from, say, schizophrenia, assist in shaping their experience of their disorder. What kind of voices they hear, what kind of feelings they have, are conditioned by how they think that a person in their situation should act. Psychosis is not just psychosis, it manifests differently according to the culture in which the psychotic individual lives.
Before Columbine, school shootings were treated as isolated events. Once they reached a certain point, however, they became standardized. Those who do them may not have specific grievances any more; they may just reach a point where they feel they've got to do something, and this seems to be what is called for.
If, however, such events start turning out differently -- if the story changes -- then the crazy, narcissistic people who might be prone to acting out this way will no longer see it as a satisfying way to stage their personal drama. One recent school shooting was quickly halted when a deputy sheriff who happened to be present confronted the shooter. The shooter skipped the middle act and went straight to the finale, shooting himself.
I think we should have police protection of schools. I am not opposed to allowing trained teachers to conceal-carry weapons on the premises. I don't see this as a panacea. I don't even see it as a permanent situation. All you have to do is stop enough of these horror stories from fulfilling their scripts, and you will make them unattractive to the people who might do them. They won't want to end their personal story that way, so they'll choose another. If you change the outcome enough times, the script changes; they will no longer imagine it working out the way they wanted. And the socially acceptable way to go crazy in our society will manifest in some other way.
That won't cure the people who do these kinds of things. But it will sure save a lot of other people from becoming extras in somebody else's psychodrama.