Even smart humans are tempted to do stupid things. If nothing stops them, the stupidity accumulates.
Under communism (and especially Communism) stupidity accumulates, because it has numerous pathways whereby stupidity is forgiven. Discipline is abrogated. Starting with the fact Communism doesn't work on paper, thus Communists always have to lie* about what they're planning to do or nobody takes them the least seriously.
The problem isn't communism, per se, but stupidity. By contrast, should a system actively persecute stupidity, it ought to be particularly anti-communist and thus particularly functional. In other words you want your society to be as Social Darwinist as you can possibly manage. No matter what downsides you find, it probably won't be as bad as letting unnecessary stupidity build up.
I don't feel I've explained this well enough, though I also can't see what I've missed. Do I also need to explain that the Sun rises in the morning? Let's try explaining the Sun sets in the evening.
Stupidity is a form of crime. Crime is fundamentally defection in the prisoner's dilemma. Stupidity is fundamentally, at best, less-cooperation, thus more criminal. Even the most agreeable stupid person has to be told what to do, because they can't/won't figure it out for themselves, which means having a stupid person around is expensive compared to a not-stupid person.
Unfortunately, yes this means some people are genetically criminal. Their existence is a crime - a net drag on every other individual they run into.
A society with less crime is necessarily more wealthy. It's really hard to find a crime-suppression technique that isn't cost-effective. If it's relevant at all and not superstition, it's worthwhile, because the more effective it is, the less you have to use it, and this self-suppression scales faster than the costs. Ideally you threaten the measure but never have to carry it out. Unfortunately the problem is stupidity, so...
P.S. Humans are Turing complete, so brain damage aside, stupidity is never a can't sort of thing. It's always merely won't. This reinforces the fact stupidity is a crime.
P.P.S. Probably not a coincidence that almost all prison inmates are stupid. Being stupid is criminal, and then also causes outright lawbreaking, just in case it wasn't criminal enough.
P.P.P.S. *How well known is it that lying is intentional stupidity? Do I need to mention this or is it obvious?
P.P.P.P.S Socrates is correct. Evil is ignorance, because cooperation is always rational. Crime is always a mistake (and mistakes are nearly isomorphic to crime).
P.P.P.P.P.S Exit is my favourite form of discipline. Sacralize Exit and stupidity will always be punished by withdrawal of agents to be stupid at.
I find stupid people hate Exit, exactly because even they realize they will be on the wrong side of such discipline. Obversely, if you're not stupid, you don't Exit a good deal. Double whammy, oof.
Intellectual laziness is isomorphic to stupidity. Do your sets.
Bonus round: Exit means what counts as "stupid" is none of my business. Don't need a Meritocratic Decider deciding what counts as merit. A) if it looks stupid but it works it's not stupid; I'm stupid for thinking it's stupid, but under Exit I can't force you to ditch the relationship, because you'll Exit from me instead. B) if it really is stupid, then I can Exit and let you wallow in your stupidity. Doesn't affect me.