Slate has an article on Adam Lanza, the presumed school shooter, now deceased. Apparently, he was bright and a good student. Apparently he was a bit odd. Plenty of people can be called a bit odd, in one way or another. We may actually learn something about him at some point, some smoking gun that he had made threats to commit mayhem, or that there was evidence that he was barking mad, but for now, there's no evidence, so the article only provides material like this:
"One law enforcement official tells the Associated Press Adam Lanza might have suffered from a personality disorder and the New York Times reports that several who knew Lanza in high school had been told he had Asperger’s syndrome, a high functioning form of autism."
He might have suffered from a personality disorder; that's not very helpful. He may have had Asperger's; several people who've met me have told me that they think I have Asperger's. I think the DSM has now defined Asperger's, as such, out of existence. Anyway, the first time a friend sent me an email about it, I looked Asperger's up, and decided that I don't seem to have full-blown Asperger's, although I'll grant a tendency that way. Anyway, most Aspergerish nerds don't murder a single schoolchild, let alone twenty of them.
What is the truth of these psychological labels, and what is the use of them? A school shooter can no doubt be described posthumously as having a "personality disorder," since no one who would do that kind of thing has a perfectly normal and pleasant personality. As Goethe put it, when understanding fails, there soon comes a word to take its place.
Compare the people you meet to the various "personality disorders" in the DSM, and you can diagnose quite a large percentage of the population. Should we put them all in locked wards? Should we have them evaluated by mental health professionals to determine which of them are actually likely to snap? Do mental health professional possess a special power to judge who is likely to snap? I believe that the answer to all three of these questions is "No." Regarding the third question, I believe that the American Psychiatric Association has pretty much admitted that the answer is "No."
We can punish criminals and we can lock up raving maniacs. To some extent, we can even treat some mental problems with medications and with talk.
We don't have a cure for human cussedness, and we don't have a good way of predicting who is going to commit slaughter, which means, alas, that we will have to endure the occasional mass shooting, mourn the dead, and offer condolences to the survivors. Meanwhile, we can at least try to keep our heads clear, and not mistake meaningless verbiage for useful information.