Psychopathy probably does not exist in the way most people think of it.
Any psychological trait that varies between individuals is distributed on a continuum whose limits are defined by the trait’s fitness benefit. This is why the personality disorders are considered dubious by some: how much sense does it make to cordon off a particular quartile, decile, centile of the distribution and declare it an illness?
Antisocial personality disorder, which most people still call psychopathy or sociopathy, is characterised by a suite of “extreme” traits, and is identified through behavioural indicators. Those are the cases that go to prison and the ones that show up in the media. But if these people’s predilections were that abnormal, they would not exist – thanks to selection pressure. The heritability of APD is no lower than the general heritability of personality, suggesting that this concatenation of traits is a (mal)adaptation.
Estimates of the prevalence of APD are on the order of 1-3%. It is not the case that 1-3% of people are violent criminals, nor that everyone in prison has the diagnosis, so it is neither necessary nor sufficient for most crime. A good chunk of diagnoses must occur because of repetitious criminal behaviour. What of the rest?
It is news to no one, of course, that most psychopaths are not criminals. The question is: what separates the criminal from the law-abiding variety?
This is a moment of revelation for some, when they have their heads scanned and realise that their neurology is “consistent” with that of a Jeffrey Dahmer. But they are not Jeffrey Dahmer. So much for the notion that it is impossible to be unaware that you have this psychological profile. Thus, they turn to parenting and other things that do not matter as an explanation to assuage the headfuck.
One hypothesis, and a testable one, is that the difference is made by IQ. One begins to sounds like a broken record, but the link between IQ and crime is well established, and given that 1 US adult in 7 is unable to perform mental operations more complex than finding the expiration date on a driving licence, it is not hard to imagine what this does when combined with a temperamental disposition towards narcissism. Not only do they feel social norms “don’t apply” to them; they are too stupid to understand the consequences of violating them.
High-IQ individuals with Dark Triad traits often go undetected or are even wildly successful. You probably know a few, and it probably isn’t worth giving them a second thought. The proto-criminal types are easier to spot, but no one wants his or her child to be branded “high-risk” before any criminal wrongdoing is committed. Nor are they prepared to confront the fact that there is essentially nothing they can do to “fix” the problem, and so nothing (useful) is done. Isn’t that just too fucking bad?