I think the idea behind Dwarf Fortress isn't to make a game where players can do anything they want, but to make a game which the player is a simulated part of, where every one of the player's decisions have a feasible impact on the game. Mass murder of dwarves is an exploit, and there's no other way of describing it: it's not
my perverted version of morality, but rather the fact that the
world is oblivious to it. All actions in the game have consequences -- you can assign a dwarf to the military and he'll get unhappy, you can send a dwarf to waltz into a pile of stink and he'll get unhappy, you can send a dwarf to kill a berserk dwarf and he'll get unhappy, you get a dwarf who watches another dwarf die and he gets unhappy, but you can't find a single dwarf that is uncomfortable with pulling a lever and crushing innocent dwarves? That screams "exploit" from every orifice.
Toady has said "you don't play the fortress, you play the world" so many times now that I feel irritated at having to repeat it. Fortress Mode is actually just a game within a game, so to speak, and based on everything I can tell DF is eventually going to focus on its Adventure mode. If moral actions matter there, they'll absolutely have to matter in Fortress mode too.
Aside from the moral issue, there's the whole issue of game balance which seems to be getting ignored here. If you can exile anyone for any reason at no penalty instantaneously, it makes the game too easy, for one, and you miss a whole lot of potential noteworthy circumstances. Where do you get the strategy of maintaining an army? Where do you get the pleasure of watching a dwarf walk up to an immigrant and talk to them, seeing the immigrant walk off with "Unhappy" status? Where do you get the occasional husband going berserk when his wife is deported, with military dwarves swarming onto the wailing dwarf as he smashes up the place? Why would the player be able to arbitrarily turn away anyone he doesn't want without using military force? (Mexican illegal aliens want to come to the United States every day, the United States has to spend considerable resources to ensure that only legal immigrants arrive.) Why would the player be able to hand out such life-shattering edicts like sentencing a dwarf to exile -- far more noticeable than just evicting them from an apartment -- when a player can't even tell a dwarf to move to a specific location without drafting him into the military and ordering him to go somewhere as a soldier?
I like the idea of registered immigration and calls for specialised immigrants, don't get me wrong... but I think that having all immigration "registered" would detract from an already interesting feature. The unplanned immigrations shouldn't be removed entirely, and should require actual shows of force to ensure that you get the process you want.
The best part about my suggested feature is that it doesn't require any changes in gameplay style as-is. If you want immigrants, you do absolutely nothing, and nothing changes from the way the game exists.
If you don't want immigrants, you have to take measures to get rid of them, and at the same time we balance out things that make no sense in a functioning game world.
If you think small scale, yeah, the fortress is yours, and mass murder might be locally acceptable, but again, you're playing the world, and dwarves on the whole have certain principles which is made pretty clear with ThreeToe's stories. If Toady can make it so dwarves can have different cultural beliefs on the morality of mass murder, I'd be all for it! You wouldn't see a goblin feeling bad squashing dozens of his brethren. He'd probably even laugh about it. An occasional dwarven civilisation here or there would also see nothing wrong with it, sure. That makes sense too. But the idea that a player can play the fortress and not the world grates on me, because the dwarves are autonomous and the player shouldn't have such a direct effect on the world's moral beliefs.