I read The Man Who Was Thursday recently. I'm still not sure what I think of its answer to the question of theodicy, but there was a bit that seemed ACKS-relevant:
The poor have sometimes objected to being governed badly; the rich have always objected to being governed at all. Aristocrats were always anarchists, as you can see from the barons’ wars.
Whether you agree with Chesterton, it makes an interesting premise, particularly if one accepts his double-meaning of anarchy as not just rebellion against temporal governance, but against natural law.
What if power corrupted, in one's campaign world? What if personal power and rulership tended to drive people to Chaos? What if kings with the epithet "the Good" were rare exceptions for a reason?
Tolkien's answer to the question "why do we need adventurers?" in The Hobbit seemed like apathetic or negligent rulers. But if the typical ruler is wicked, it is even less surprising that the plight of the peasants whose goats are being devoured by gryphons is ignored by the powers that be, and they are left to petition adventurers. It also explains why in OD&D lords shake down adventurers for magic items, and archmages and high priests geas/quest them for the same.
It provides a great justification for PCs to overthrow existing rulers and take their stuff, while posing new hazards to be navigated.
The naturalistic take is that when people acquire power they gain the freedom to indulge their vices and to surround themselves with people who won't stop them. There is also a Sword of Damocles angle, where rulership is insecure and so rulers tend to grasp at any and all means of holding on to power, including dangerous ones. Selection effects and the Iron Law of Bureaucracy could play a part as well - those who rise to the top are those who are willing to use all means available to amass power, not those who are honest and just.
The McLeod Company Hierarchy also springs to mind
To some extent we already see this happening to player characters without codifying it. PCs have a notorious tendency for wanton disregard for NPC life and property. Want of money is the root of all evil, and money gives XP, so... the incentives line up. We also see it a little as a side effect of the Tampering with Mortality table; gathering XP is dangerous and many PCs have close calls which lead to some spiritual deterioration. And certainly I have seen PCs rule their domains with secret police and iron fist.
It's funny, that I think this was actually the first I ever heard of Seeing Like a State, and it was about strategy gamers behaving badly.
Mechanically, how might we rig the system such that rulers tend to be bad? One simple approach is to flip ACKS' random alignment generator, which was on a d6, 1 Chaotic, 2-4 Neutral, 5-6 Lawful. But maybe for rulers, you do 1-2 Chaotic, 3-5 Neutral, 6 Lawful.
Renegade Crowns' prince generation system tends to produce rather flawed characters. It is possible to generate one who is a decent person, but rare. Renegade Crowns' domain engine also turns domains into a source of trouble, hence into temptation to seek additional power to keep a lid on things, maybe without reading the fine print.
If you like numerical corruption point accumulation systems, you could certainly wire one up so that leveling incurs corruption. I don't like such systems, personally.
AD&D suggests a less dissociated alternative - for high-level assassins and druids, leveling is a zero-sum game, where you have to go topple the previous Master of Assassins or Arch-Druid in order to level up. Zero-sum games always bring out the nastiest in people. A very Damocles situation for the current Master, one in which he is strongly incentivized to accumulate as much power as possible to secure his position, and one in which challengers are likewise encouraged to play dirty. Imposing similar diegetic requirements at lower levels could be an option.
(What else could we make zero-sum? Spell acquisition, by removing copying? Magic swords, by removing crafting entirely?)
Dark Sun and ACKS suggest another angle, with the ability to surpass the limits of human power by abandoning humanity through undeath, apotheosis into a dragon, etc. If you lower the limits of human potential to, say, 9th level rather than 14th (or even down to 6th), committing crimes against the natural order to surpass human limits becomes much more pressing.
What does a world built with this idea as a premise look like?
Kings and princes are fearsome and dangerous and mostly view people as means, as tools to be used. Their servants and courtiers and lieutenants may be complicit, or scheming and striving, or just doing what they have to do to get by, or believe that though what they do is repugnant, it is for the greater good. Down at the bottom, the peasant, the pickpocket, the bartender, and the guard at the gate are basically decent. They have no power, and so no corruption. There is honor among thieves, as long as they are little thieves. But if they get too big, then the knives come out.
Maybe loyalty score modifiers for hirelings based on level could use some changes to match these assumptions.
But I think this is an important differentiator from grimdark. In grimdark, even the little people are often basically bad - untrustworthy, cruel, vicious, spiritually ugly. Needn't be so.
What do gods and churches look like in such a world? If your high priests are cynical and power-thirsty, are the gods ambivalent about the moral qualities of their priests? Or are the gods themselves caught in the same traps as high-level characters, perhaps even just ascended mortals? Do even "good" gods demand great sacrifices of their worshipers to maintain their position against their divine adversaries? Are they just so alien that they recognize neither natural law nor human morality? Are they demiurges, tasked to maintain the work of a now-absent creator deity but falling away from their original purpose and natural law over eons of hard decisions and unsatisfiable constraints?
