Maybe one of the reasons (fittingly remembered on the 4th of July) that a republican democracy works better, on average, than an aristocracy is that it makes no special assumptions about the virtue of the rulers.

Actually, this is a first tier implication of Bruce Bueno de Mesquita’s “Logic of Political Survival”, which I strongly suggest you read. He builds testable theses out of the core axiom that politicians first and foremost want to gain power, and once there they want to keep it.