> The issue observed over millennia, is that if you get rid of -all- the greedy people in your land, the greedy person in charge of next door sees opportunity.

I don't see why that necessarily follows. What you describe is the ability to defend oneself: If you become so weak and/or pacifist that you can't even employ violence against attackers, then, yes, someone else will take your lunch.

Whether or not the ability of effective defense also requires the drive to attack others out of greed is, I'd say, still an open question, even though lot's of people have their own preferred answers.

I'd argue, evolution iself shows lots of counterexamples: If the assumption would be true, then only predators should have survived until today. But that's not the case: We have lots of herbivores that can defend themselves against predators but aren't ones themselves.

Whether or not this holds for humans is a different question and the current "experimental evidence" isn't exactly encouraging: Attempts to build a different society were either not strong enough to defend themselves (paris commune, spanish republic) or were strong enough but got corrupted once again by the drive for greed and power (christianity, the soviet union).

Still, on the other hand, I think overall, humanity has become less aggressive and the social value of war has changed: It used to be a virtue in itself (as discussed in the OP) and today is mostly outlawed and, if at all, seen only as a valid tool for self-defense. That could at least make one hopeful, even though enough decidedly nondefensive wars are still being waged in the world.

> My more specific suspicion is that some of it is that those who can 'go with the flow' are more likely to survive various 'cleansing's over the ages, and perhaps in fact the most 'opportunistic' (i.e. those that are not -quite- megalomania tier) find those opportunities and become that sort of 'old money bottom feeder' type.

That's the darwinist explanation. I still think there are some specific psychological mechanisms that facillitate those social dynamics (and I'd be interested to know if they have a neurological/genetic origin - which might have evolved due to the selection dynamics you derscribe)

Some of those I can think of:

- Ingroup/outgroup bias:

That one is well known, basically the tendency to sort the people we interact with into two groups - often by completely arbitrary attributes. Our sense of empathy and compassion for both groups is wildly different.

(In reaction to this tendency, I actually find the cheesy "we're all brothers/humans/citizens of Earth/children of God/etc" calls actually quite smart: In essence, they try to trick the ingroup/outgroup mechanism by just defining everyone as the ingroup. It's a simple strategy, but there is no obvious reason why it shouldn't work.)

- "Groupthink" (when interacting with the ingroup)

The tendency to judge decisions differently if you do them as part of a group or for someone else within that group instead of yourself - and it has the unfortunate tendency that it lets you do far more morally questionable and risky decisions without appearing as morally questionable.

A harmless example would be buying christmas presents: There is lots of stuff that you would never buy for yourself, because it would seem like selfish and frivolous spending - but you readily buy the same thing for someone else as a gift, even if the purchase would objectively be just as unnecessary.

A more serious example would be conquests: Everyone understands that just breaking into the house of another person and taking their stuff for yourself is morally repugnant. But if your group violently takes land, it's suddenly justifyable, because it's for the good of the group and not for any individual person.

(Thanks to ingroup/outgroup bias, both sides of the conflict will experience and judge this in a radically different way: The conquering group will be quick to justify and forgive itself while the group that was being attacked will see it as a grave injustice and breach of moral)

- "Sadomasochism" (when interacting with the outgroup)

I don't mean that in a sexual or deviant sense, but just as the property that knowingly causing harm to others or imagining how someone else is being harmed can sometimes feel good - which really is odd if you think about it: We're well aware of how bad harm feels and usually we avoid it at all costs. So, naively, we would think that there is a simple connection in the brain that says "(things that you know causes harm) -> stay away from". But in reality, the relationship is much more complex and depends on the context and who is experiencing the harm.

- "Leader worship"

One example I have seen of this that came to my mind was when a new pope was elected: Some relatively unknown (outside church circles) and colorless cardinal went in; then it was announced that this person would become the new pope; when he showed in public the next time, millions of people around the world already had made an intense emotional connection to that person and were ready to take their word as law - only by announcement of his new office and without actually knowing him.

I think you can see the same psychological effect in many parasocial relationships, bei it for streamers, celebrities, royalty, politicians or religious gurus.

I feel as if those mechanisms form some of the "environment" in which a "dark triad" person could actually gain and realize power. They also form an environment in which millions of people would be ready to do something as paradoxical and self-destructiva as to wage war.