There seem to be some interesting similarities between psychopaths and ethical egoists.
Based on the stock account, a psychopath has a deficit (or deviance) in regards to interpersonal relationships, emotions, and self control. In terms of specific deficiencies, psychopaths are said to lack in shame, guilt, remorse and empathy. Robert Hare, who developed the famous Hare Psychopathy Checklist, regards psychopaths as predators that prey on their own species: “lacking in conscience and empathy, they take what they want and do as they please, violating social norms and expectations without guilt or remorse.”
Interestingly enough, these qualities also seem to describe the ethical egoist. Ethical egoism is an ethical theory that individuals ought to maximize their own self-interest. This is generally contrasted with altruism, the view that people should (at least some of the time) take into account the interests of others.
Ethical egoism can also be cast in more general terms as a form of consequentialism. On this sort of view, people should maximize what is of value (V) for the morally relevant beings (MRB). The sort of utilitarianism endorsed by Mill is a form of consequentialism. However, Mill is clearly not an ethical egoist since he considers all humans (and sentient beings) as morally relevant beings. In the case of the ethical egoist, the scope of morality (who counts as a MRB) extends only to the individual. For example, if I were an ethical egoist, then the MRB would be me (and me alone). If you were an ethical egoist, then your MRB would be you (and you alone). As far as values goes, V could be almost anything. However, it tends to be things like self-interest, pleasure and happiness. Famous ethical egoists include Glaucon (as laid out in his Ring of Gyges tale), Ayn Rand, and Thomas Hobbes.
While this oversimplifies things a bit, those who accept ethical egoism generally claim that people are naturally inclined toward desiring “undue gain” and are not naturally inclined towards sympathy or goodwill towards others. Hobbes makes it rather clear that people are lacking in sympathy and are motivated only by the hope of gain and glory. In many ways, this view seems to cast humans as naturally exhibiting some of the key traits of psychopaths. It is no wonder, then, that Hobbes argues that people do not form society out of mutual good will or on the basis of being social beings. Rather, people form society out of selfishness and it can only be maintained by the power of the sovereign.
However, what defines the theory is not the description of humans but rather the prescriptive element. Proponents of ethical egoism endorse the claim that each person should act so as to maximize value for himself. Rand goes as far as to cast selfishness as a virtue and altruism as the height of foolishness. In a way, it could be seen that Rand is advocating that people act like psychopaths.
Of course, there are important distinction between being a psychopath and being an ethical egoist. One is that psychopaths are supposed to behave in ways that are impulsive and irresponsible. This might be because they are also characterized as failing to properly grasp the potential consequences of their actions. This seems to be a general defect in that it applies to the consequences for others as well as for themselves This reduced ability to properly assess the risks of being doubted, caught, or punished no doubt has a significant impact on their behavior (and their chances of being exposed).
If Glaucon’s unjust man is taken as a role model for ethical egoism, the ethical egoist is supposed to strive to be the opposite of the pyschopath in this regard. The successful unjust man is supposed to grasp the consequences of what he does and hence acts in ways that are calculated to conceal his true nature. The unjust man is also supposed to have the impulse control needed to act in ways that make him appear to be just. It is tempting to conclude that an ethical egoist is essential a psychopath would good impulse control and a grasp of consequences. Or, put another way, that a psychopath is an ethical egoist who is not very skilled at being an ethical egoist.
Interestingly, when Socrates gives his rebuttal to Glaucon, he argues that the unjust man actually does not grasp the true consequences of his actions. That is, the unjust man does not realize that he will corrupt his soul in the process of being unjust. If so, perhaps the ethical egoist is a psychopath with an ethical theory.