Purely academic attempts at measuring psychology have been making progress over the years, assigning various scores to various traits and likelihood of affliction and reform, but they're far from a hard measurement and seriously prone to bias.
Perhaps we should ignore obviously mentally ill criminals and disarm those that have never comitted an act of violence. I mean, since there is no way to even identify lunitics we should just give up on the concept and move on to disarming those that have never done anything remotely resembling a violent crime.........
There's no upside in politics to going to bat for criminals, and if you take steps to issue a pardon or revise the law, and somebody in fact does repeat. Kiss your political career goodbye
Tell that to your good governor, Jesse Jackson, Barbara Boxer, Diane Feinstein and a boat load of others....They aint batting criminals, just their careers.
Psychology is too new and soft to be used in any significant way in legislation. It does far more damage than it does any good.
Far more nebulous than the science of global warming for sure.