It’s less about the fallibility of humans, and more mathematical than that. A person ability to acquire wealth is proportional to the current wealth they have. (And I’m not just talking about money, I’m taking about resources and power) As a result, those with a tendency to act nastier have an advantage in gaining wealth. This same issue is present in a communist economy, because while communism eschues the concept of money, it does not reject the idea of unequal power. Even some super intelligent AI wouldn’t be able to fix this, as long as it was forced to give humanity basic freedoms and follow communist ideals.
Honestly, this whole communism vs capitalism debate is beneficial to the powers that be, since neither system actually tries to prevent the acquisition of power or the abuse of it.