Referring back to the "why choose evil" thread, it is evident that those who choose evil are choosing Ni over Si, and in a very specific context. The superego functions command that you consider your impact on others' experience of them when affecting its elements with your ego block. Say for example, I may act to improve my Si, but if it is at the expense of others' Si some would call that evil. Most people would consider weighing the social costs of the Si vs the personal costs, trying to find a balance via universal ethical egoism (a concordant person might resort to altruism) and sharing knowledge of this balance. A personal egoist presumably cannot find this balance for themselves, and must receive awareness of it from others. An individual egoist will always look for the altruistic frame offered by the other side's ideology (their morality), because it offers a rationale for unmitigated scorn and hate. However in lieu of this balance they will act indifferently to the superego block, or even totally against it. Or if they are smart, they will use one side's moral gaps as a shield by which to cover themselves as they pursue their indifferent interests, thus enabling them to escape the superego's vise to their satisfaction. (this is apparently how dictators do it, the practice of "charismatic sociopathy")
Psychopathy is the bid to do as much social damage as possible. It is a deliberate act of defiance against social norms. The point of psychopathy is not just to do what one wants in spite of the consequences -- it's to spread the gospel of social indifference and to create more and more indifference to others' status. It is the cause of social destruction. Don't just be content that you have chosen to pursue naked self-interest... make sure that others feel they must take the same course. This in the non-totally insane sense of psychopathy. In the insane sense you have all the features of the messianic killer, combined with an urge to perpetuate this standard of belief. Gadhafi showed us what this looks like a few months ago, however the Columbine killers offer a simpler (and rarer) picture of the phenomenon, in that the Columbine killers were driven by rage without a developed social core, thus they exhibited oppositional defiance exhibited, and thus exhibited unrestrained destructive rage (although I hear they were harder on the Christians than other members of their Mafia). The point of psychopathy is destroy a specific society outright.
Variants of Psychopaths
Creator type: the creator type psychopath (ethical psychological egoism) specializes in increasing the indifference around them by appealing to their peers to be indifferent to those they meet. In their view, people cannot rely on each other. The idea that they can is a lie that must be expelled. The more severely their abandonment in the past, the more severely the ethical psychological egoist believes that love is a lie.
Destroyer type: the destroyer type psychopath specializes in creating distrust, so that concern by others for each other degrades into indifference. By creating distrust, they make others more reliant on them. The aim of the destroyer psychopath is to be the only one trusted, and so be the only one relied on for upholding social responsibility. This in turn is the pathway to power. In a world without love, social responsibility is key. Self-interest is the bedrock of the state.