Ah forget about it. I don't see why there couldn't be anarchist systems in df. I tend to view dwarves to be fairly anarchic in the way their society actually works. Also for a short time a people could be anarchist but then they are run over by other systems due to their inability to act quickly.
The reason is that Anarchism is pretty much impossible for the game to actually model, in the sense of
Agent Smith in the Matrix "some believe that we lacked the programming language to describe your perfect world,". The reason is that even if Anarchy were possible realistically, it is still not possible for the game to model an order somehow emerging from the individual decisions because of how individuals do not exist when we are not there. How does a large number of people make decisions 'anarchistically' when they are not loaded to make those decisions?
I'm pretty sure that there are lots of versions of Anarchism, and none of them promise everything to everyone. They just claim to be a better option than the alternatives. Sure, you can probably find a few individuals who will promise everyone that anarchy will make their lives perfect, just like some insist that the free market will solve all problems if we just get out of its way, or the government can fix everything if given the chance. But that isn't part of the actual political philosophy behind it - just advertising.
Also, DF is a fantasy world generator, not a political science research simulation. It should be able to handle a wide variety of social and governmental structures, including ones that probably wouldn't work in reality, because lots of fantasy settings include societies that aren't very plausible.
It is not a question of whether it would work or not. The free market does not work, unless you are a sociopath indifferent to human suffering but the free market is a coherant logical system; what it's proponants are saying is internally consistant. Anarchism is completely illogical, it is the political equivalent of
"have your cake and eat it too" as I said before; that means that a computer, as with reality cannot represent Anarchy as the Anarchists propose it.
The reason it is illogical is that Anarchists are both Socialists, therefore opposed to the free market and also opposed to government, hence in favour of the free market. Free market happens whenever we have two independant parties not subject to the regulation of a common authority. For instance, despite the total lack of any free market internal to the fortress, the exchange between the fortress and the caravan operates according to the free market. This is not a question of what either party believes, presumably the dwarves do not believe in the free market but a question of the fact that both are equal parties that are not subject to the regulation of a third party means the free market applies regardless of what they believe in.
If we got rid of all the positions and had the dwarves decide what the fortress does collectively without any positions; then we would still have Socialism, but we would not have Anarchy because it is fairly clear that the individual dwarves must still obey the authority of the fortress for things to work. If we made things work pretty much as they do in Adventure mode then we would have the Free Market, meaning that even though there is no Authority there is no Anarchism either.
Goblins aren't a unified force. They routinely murder each other. They only seem to unify when their leader or an outside threat forces them into it.
Mobs would generally be temporary, focused upon a specific issue or conflict, but the most powerful networks of cooperation and loyalty probably would develop into something rather like a local government. When there are several large networks in the same site, I'd expect a lot of scheming and a bit of skirmishing to get more power within the site, but they'd usually avoid the sort of outright warfare that would attract the ruler's attention and is likely to get all the leaders swatted down.
It's all well and good to say that goblins who cause too much trouble get defined as traitors, but defined by who? If they annoy the ruler, the ruler can declare them a traitor and mobilize everyone against them. But short of that, it's just going to be the individuals who don't like them or consider them a threat, trying to convince enough others to act that they can overwhelm the problem's supporters or intimidate them into switching sides. In that context it doesn't matter much if the accusers are appealing to ethics against treason or to self interest.
Goblins routinely murder each-other. That however does not mean they are not a unified force, in fact not so long ago it was entirely legal for people to have duels and kill each-other entirely legally. Goblin murders are less honorable but essentially they are the same, that the idea that individuals killing other individuals and being allowed to do so means no unified society is not correct.
The goblins would be defined as traitors by the goblin judge. That would basically be the only crime on the book, all crimes would be considered forms of treason and all crimes would be punished with death. Individuals would be free to steal from and kill from each-other, but if they do anything more organized they would be executed as traitors, since their actions are now undermining the goblin state/society.
The word I've seen that best describes the way vanilla goblins seem to operate is kratocracy - rule by the strong. Authority rests with individuals who can manage to seize power, be it through force and threats, skillful negotiation and dealmaking, or sheer charisma and persuasion. The overlord has control because they're the strongest of all.
In other words, they are a government.