George Wallace said:
Or institutionalize them when diagnosed.
You're assuming that most of them get diagnosed. Afterwards, you can maybe find some people who will say; "Shucks, he did seem a little off." But that's about it.
A lot of these folks go unnoticed because staying under the radar is a huge perk if you can manage it in today's world for a lot of people and a frigging survival skill for some.
A lot of them go unnoticed because their mental state isn't that unusual in a society where 1 in 3 people come from fatherless homes and where almost a quarter of young men are put on behaviour modifying drugs at some stage of their schooling.\
George Wallace said:
Or institutionalize them when diagnosed.
At heart though George; you're talking prevention, which is nice when you can do it, bot just not all that reliable and I'm talking mitigation; which is the reality of a society in which things like this happen and will keep happening until we have real, serious social change that;
a) revolutionizes how we view and treat mental illness.
b) stops the war on men and boys and makes it okay, even admirable to be masculine again.
c) deals with the scourge of fatherlessness; a trait which runs in common through virtually all school shootings and the vast majority of violent and career criminals.
I'm not personally sold on whether the guy was really a wannabe terrorist anymore, so I'll leave that aside for now. Hell, I've got the Red Hand and Erin Go Bragh hanging side by side right next to me and I study the Troubles and that hardly makes me a terrorist.