We have argued here that to attribute criminal responsibility to psychopathic individuals is to ignore substantial and growing evidence that psychopathic individuals are significantly impaired in moral understanding. They do not appear to know why moral transgressions are wrong in the full sense required by the law. As morally blameless offenders, punishment as a basis for detention cannot be justified. Moreover, as there are currently no successful treatment programs for psychopathy, nor can detention be justified on grounds of treatment. Instead, we argue detention on the grounds of self-defence, due to the severe and continuing threat posed by the psychopathic criminal. Acknowledging that the psychopathic offender is not criminally responsible would clearly have significant implications for their treatment in the judicial system. Moreover, explicit acknowledgment that psychopathic offenders are selectively but significantly mentally impaired might act as a motivation for the development of much-needed, targeted, treatment and management programs. We do not deny that psychopathic offenders are dangerous and 'calculating predators' (Hare, 1998a, p. 205). However, to ignore the substantial evidence that psychopathic offenders are not criminally responsible is itself a dangerous threat to criminal justice.