The most compelling reason that I’ve come across, and I’ll see if I can find it again, was a paper comparing American and European culture in relation to how well an individual felt a connection to their community. Now I read this paper in college, so I can only offer the summary as I remember it, but basically the gist was that Americans, due to a highly mobile society, don’t tend to interact with neighbors or others in the community on a deep level. Americans tend to view their community more in terms of who their friends are, not who lives near them. Europeans, on the other hand, tend to have a more localized view of community. Those who live near you, even if they aren’t really friends, are people who you should take an interest in. This paper theorized that rehabilitation for prisoners works better in Europe because the inmate leaves prison for a community that will take an active interest in them doing the right thing. So in Europe a neighbor would be more likely to intervene early, if they know there’s a problem, than an American who may not know their neighbor is having a problem until it’s too late. This would apply to school shootings, or really any sort of horrific crime in the US, for many of the same reasons. Take that family in California who locked their kids up. The neighbors said pretty much all the same thing “Quiet family, kept to themselves, didn’t really know them”. That same sentiment gets said about school shooters. No one in the community outside a small handful of people really seem to know anything about the shooters. I saw this when I was working in mental health as well. I would have clients, just 8 or 9 years old, who would run away from home, or self harm. I can’t think of a single neighbor of any of my clients who knew anything about what was going on with them. This isn’t a criticism of American culture, it’s just the byproduct of a huge, diverse, population that’s likely to move on a more frequent basis than Europeans, but it’s something that needs a solution to if we want to improve things like mental health, crime, rehabilitation of prisoners, etc.