Psychopaths aren't capable of empathy. Having knowledge of something doesn't mean having an understanding. I know how you feel if you tell me how you feel. I don't understand how you feel unless I relate it to how I felt when in your position.
An fMRI study of affective perspective taking in individuals with psychopathy: imagining another in pain does not evoke empathy
There is general consensus among theorists that the ability to adopt and entertain the psychological perspective of others has a number of important consequences, including empathic concern (e.g., Blair, 2007; Batson, 2009; Decety and Svetlova, 2012). Adopting the perspective of another is a powerful way to place oneself in the situation or emotional state of that person (Batson, 2011). Our results demonstrate that while individuals with psychopathy exhibited a strong response in pain-affective brain regions when taking an imagine-self perspective, they failed to recruit the neural circuits that are were activated in controls during an imagine-other perspective, and that may contribute to lack of empathic concern. Finally, this atypical pattern of activation and effective connectivity associated with perspective taking manipulations may inform intervention programs in a domain where therapeutic pessimism is more the rule than the exception
Of course the above experiment is a bit flawed but it does indicate that psychopaths do not experience empathy in the way neurotypicals do. It is equivalent to saying that psychopaths have a diminished capacity for understanding certain cues and signals.
A proper psychopath never acts impulsively or is driven by his own anger. That's why he can be so manipulative and powerful.
Psychopaths by definition are impulsive or they wouldn't be clinically diagnosed as psychopaths. Also, the human you describe doesn't exist. Any psychopath is also a human. Any human also has emotions, and which emotions the human will respond to differs from person to person. A psychopath without a short temper might easily get jealous, or may be tempted in many other ways away from rationality. The fact is, the idea of "proper psychopath" like you see in series like Dexter is not based off reality. If you look at actual clinically diagnosed psychopaths, you will never find a "proper psychopath" immune to being manipulated.
Finally I will note, anyone can be manipulative and powerful. Psychopaths do not have a monopoly on being manipulative and powerful. Manipulative is a learned skill, and power is acquired. Terrorists and gangsters can be manipulative and powerful, but not necessarily psychopaths or rational.
References
- An fMRI study of affective perspective taking in individuals with psychopathy: imagining another in pain does not evoke empathy https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3782696/
The only important thing here is that psychopath knows what you feel and makes use of this knowledge to his own advantage. And my point is that in statistical terms this is the most rational behavior one could imagine.
My point is everyone does that, not just psychopaths. Psychopaths simply manipulate in a particularly callous way is the main difference. But just as every person has told a lie, every person has manipulated someone else. And who doesn't use knowledge to their own advantage?
So unless there are people who never lied and who never use knowledge to their own advantage, I guess I don't see the point to bringing psychopaths into it. Sure psychopaths manipulate but so do law enforcement investigators/interrogators.
My point is you can be rational or irrational without being a psychopath so really that doesn't have anything to do with being rational. You can also be ethical or unethical being a psychopath or not so that doesn't have much to do with ethics.
You still don't get the point why we started talking about psychopaths. The point is this: their behaviour is morally bad yet can be perfectly justified on the rational ground.
All this is to prove the point that morality cannot be derived from rationality. Even worse, moral acts which receive the most admiration are completely irrational.
To give a simple example: if I find a wallet in the street the moral thing to do is to try to find the owner and return it to him. Yet the rational thing to do is to keep the wallet and spend the money.
Unless you can to prove that being egoistic in this case is irrational. Good luck with that! It's morally bad but not irrational.
Their behavior can be wise and rational or unwise and rational. To be wise is to take a long term view of your own future when deciding on a behavior. If you take a short term view, similar as with investments, you're pretty much gambling. When you gamble you might gamble based on some rational theory but you typically lose long term and this is what happens a lot of the time with psychopaths who as I said have great difficulty taking a long term view.
A narcissist who follows a wise strategy can be perceived at one of the most moral people in society whilst also being completely rational and selfish. Narcissists can manage this because narcissists care a lot about how other people perceive them and this is a key difference which in my opinion is the real thinking behind moral behavior. The moral behavior is something an individual adopts in order to be perceived a certain way by others in society whom they respect or seek the respect of. So it's actually rational behavior to adopt moral behavior but only if you take a long term view and think long term.
I don't have to do that. I can show you that you can be rational but have a short time horizon or you can be rational and have a long time horizon. If you don't believe you are going to live more than 5-10 more years you might not have any reason to care about social conventions of society or adopt the moral norms of your community. But if you do intend to live beyond 10 more years and you intend to stay in that community, then it becomes rational to adopt the moral norms of that community. There is no reason other than rationality to adopt moral behavior in my opinion and if it is irrational to be moral then I would think a lot of people wouldn't be. Going against the moral norms is essentially taking a bet, and there is risk and reward with any bet.
References
This is not necessarily the case. My argument is there is no fixed set of "moral thing to do" that everyone is born just knowing. People discover the "moral thing to do" by trial and error or by observation. The reason people do the "moral thing" is so they can be perceived as a "moral person" by the "moral community". There is no inherently moral thing to do, but there is a normal reaction. Most people will want to take the normal reaction regardless of whether or not they agree with how it feels. Conformity is what is behind morality.
If someone found a wallet and there is no possibility of it ever being detected in the future by anyone that they took the money then a lot of people will take the money. Why? Because the risk vs reward ratio would skew far in favor of taking the money. But if a person seeks respect from the moral community (people who apparently think like you do) and the odds of it being detected that they took the money in the future are high that it could get back to you someday, then they will not take the money so as not to ruin how you perceive of them and so as to not harm their reputation.
The individual we speak of does not need to have a feeling one way or the other about the owner of the wallet and merely has to think about their own consequences to take either action A or action B. The risk vs reward ratio in my opinion determines what action a rational consequence based person might take but even that might not always be the case as a rational consequence based person isn't rational 100% of the time. Say for instance if they know the person who owns the wallet and it's their friend, well now they might not be as rational.