It is common for philosophers to argue that psychopaths are not morally responsible because they lack some of the essential capacities for morality. In legal terms, they are criminally insane. Typically, however, the insanity defense is not available to psychopaths. The primary reason is that they appear to have the knowledge and understanding required under the M’Naghten Rules. However, it has been argued that what is required for moral and legal responsibility is ‘deep’ moral understanding, something that psychopaths do not (...) have either due to their lacking empathy or practical reason. In the first part of the paper, I argue that psychopaths do not lack the abilities required for deep moral understanding, although they have deficits in those areas. According the M’Naghten Rules, therefore, psychopaths are not insane. Under a less strict formulation of the insanity plea, like the Model Penal Code, however, there is a good case to be made for their lacking substantial capacity. I argue that because psychopathy is an essentially moral disorder, and because of the nature of psychopathic violence, psychopaths should not be excused under the insanity plea. It would be tantamount to excusing someone for committing a crime because they are bad. Arguably, this contravenes the entire system of law. (shrink)