If only we had a test!
Then we might be able to identify psychopathic, sociopathic, histrionic, narcissistic, borderline, paranoid personalities before they do their damage.
A land of liberty must always balance the extremely high value of individual self-determination against the extremely low possibility that the average sociopath might go full pissed off postal jihadi. Err on the side of freedom and accept some collateral damage is wisest.
A note in the file might help law enforcement triage their welfare-check stops when they have complaint after complaint about some individual.
Every time I receive a voter information pamphlet I think how much more informative than personal statements would be to have in addition each aspiring public servant's score on the PCL-R. It might serve to weed out some of the worst before they are able to do their worst, anyway.
Public policy kills more people (1788 per day in USA in 2014) than guns or knives or any other thing. That killing goes on every day on a massive scale. And that's just one kind of murderous public policy. (Consult your average Venezuelan for other examples.)
Test all candidates for public office. Publish the results. Let's start there. It's time we enacted common sense measures to help stop the violence. Once we get the politicians sorted out, we can talk about testing some of the discipline-problem kids in schools; by then we should have more reasonable policy makers to carry the torch of liberty as well as "safety."