If Robert Hare and others are correct and psychopaths have different EEG signatures from normal people, then it might actually make sense to devise some sort of foolproof test for it and brand these people with a capital 'P' on their foreheads or something like that when they're five or six years old so the rest of us can have an easy time avoiding them.
In the case of Paul Bernardo, the total price tag for having one psychopath being unrecognizable comes to a couple of dozen brutally raped women, at least three dead bodies and probably more like five or six, one totally innocent guy (Baltovich) spending eight or nine years in prison for one of Bernardo's murders and still facing a second trial without anybody saying word one about questioning Bernardo on the matter, and a woman just now getting out of prison after twelve years for her part in this whole mess which almost certainly involved brainwashing or something entirely similar to that.
That's too high a price for to pay for whatever political correctness might arise from having defective people walking around unmarked and undifferentiated.