The topic was mentioned back at the List of Remaining Items -thread some time ago, and I started thinking about it. Probably more deeply than is healthy. I was never able to resist the siren call of xenosociology. Anyway, I think it could be implemented, but in a way that would address none of the reasons people would want it implemented in the first place. That's the reason I'm posting this here, by the way, and not the suggestions forum. I guess this would be sort of neat but there's not that much to be gained from actually putting it in the game. And unless I post it somewhere, my head might explode.
So. On one hand it was mentioned that ordering a dwarf to go and kill another dwarf goes against the design philosophy of controlling the fortress, not the dwarves; while on the other hand, it might be really useful and fun sometimes, and there are ways to kill dwarves whether or not it's "allowed". And to be fair, examples of governments choosing to arbitrarily murder some of their own citizens aren't that hard to find in the real world. If the player wants his fort to be a fascist nightmare state, I don't see any point in stopping him.
All that needs to be done is to make sure that there are appropriate repercussions for trying to kill everybody. Running a fascist nightmare state shouldn't be easy.
Only the ruling class is allowed to kill people.
Examples of peasants putting their masters to death in a calm and organized manner are significantly less frequent than the other way round. In practice, this would mean that you can't order any nobles to be killed, and you need nobles around to kill anyone. You would at least need a hammerer, and some high-ranking noble. Maybe if the execution orders came from someone ranked below the king, the higher ups might disagree with this and do something.
(This would render most dwarves the player would actually want to be rid of untouchable. Especially the hammerer, since he's the one performing the executions. Clever, huh?)
Killing people causes a lot of unhappiness.
The duke signing the imperial proclamations would obviously not take any action against anyone he likes. The hammerer lives only for justice, but he wouldn't like it. And the rest wouldn't get just the usual unhappy thoughts that can be removed with a pretty waterfall and a nice dining room. Abducting people and hammering them to death for no reason at all should cause deep-seated resentment against the government that wouldn't go away within a reasonable timeframe. The people might forget and forgive eventually, but it would take a few decades. And that's assuming you stop killing them.
The guards, and other people directly employed by the dwarven government might refuse to work if you oppressed any of their friends. The guards would be necessary, too; unless you make a show of being more powerful than the underclasses, they'll just start rioting, thinking no one will stop them. And the citizens would be constantly angry, temporarily kept docile by the pretty waterfall and the nice dining room, but ready to turn into an angry murderous mob if things suddenly took a turn for the worse. You might even get occasional assassination attempts on the ruler.
And if you let the situation get out of hand, you'd have a bloody civil war on your hands. If the nobles, backed by the guards and hopefully the jaded veteran members of the army, manage to win, you've just lost a good share of the actually useful dwarves who get things done in your fortress. If the peasants win, you've still lost a lot of useful dwarves, your military is quite possibly decimated, and the mountainhomes will be distressed at this new turn of events, and try to fix the situation by sending a new batch of nobles. and if the new nobles are not accepted and obeyed by whoever was in charge of the newly liberated anarcho-syndicalist commune, a siege.
All this might even occur without the player intending it, as a natural result of all those hammerings from failing to fulfill a mandate. So the punishments for those might have to be toned down a bit, with the noble in questing getting to choose whether he wants to punish anyone, and punishments ranging from a disciplinary hearing to jail time to death. Actually, maybe this should be done even if the reactions aren't worsened.
---
The framework for some of these things might actually exist after the army arc is done. One of the stated goals is allowing conflict over succession, schisms and contested claims to entity positions, and this might potentially include the concept of a civil war, perhaps even inside a single site.
All this would probably just result in half the players running fascist nightmare states just because they can and frequently having their population wiped out by revolutions and tantrum spirals. So, new ways to be evil and new ways to lose. Just what the game needs.