An ideal HE behaves rationally, yes, but that doesn't tell the whole picture; being rational is about discussing with oneself all the possible behaviours, choosing the one that gives him the outcome closest to his desires. But also, and this is very important, it seems like the only thing an HE cares about is his own benefit, especially his own monetary benefit. So he has friends only because "who you know" is valuable and can help him get more money; he doesn't care about poor people because their misery doesn't affect him; the welfare of society in general is not relevant unless he can benefit from it; etc. Many people, including me, find all this very troubling, since this is the kind of people that makes this world far worse than it could be. And yes, I would say that it's clearly psychopathic behaviour.
Some economists that present, either tacitly or openly, the HE as a positive ideal, try to hop over this troubling issue by using the ill-defined term "utility", saying that an HE is someone who maximizes the perceived utility; and then they proceed to basically define the behaviour of the HE as economically-oriented, making the whole "utility" concept useless.
Contrast with this Marxist slogan: From each according to his ability, to each according to his need. One can be perfectly rational and follow it; it's just about using reason to fulfill a completely different goal. So being rational is about means to attain a goal, while being an HE also includes the goal of hoarding money and not caring about what happens to other people.