Archetype: There aren't a lot of revolutionaries in fantasy fiction -- or in fiction in general, that I can think of. When they do exist, they are freedom fighters working against a tyrannical empire: The Rebel Alliance of Star Wars
Real-Life Inspiration: Obviously, the Faberists are based on historical revolutionary groups, most notably the Soviet and Chinese Communist revolutions and the French revolution. The biggest thing I take from historical studies of these groups (which, to be fair, I have only cursory knowledge of) is that they were all filled with radically different opinions on which direction to take the new government. One only needs to look at the contrast between the beliefs of Lenin, Stalin, and Trotsky -- or between Mao and most of his contemporaries. In fact, all three of these revolutions, as well as the American Revolution, started out with one government, which then collapsed before stability could be achieved.
And thus, the Faberists' greatest weakness -- they cannot decide how far to take their revolution, or in which direction: some wish to burn it all down and start from scratch, while others merely want to perform relatively minor governmental rejiggering. Without a single influential leader, their infighting may doom them to never finding, let alone achieving, a singular goal.
Theme: The Faberists are about idealism and dissatisfaction. Though they are unable to agree on how the City should be changed, they all know it doesn't work the way it is. They are fundamentally incapable of just living their lives and letting the City go on in its flawed fashion, and those passions and ideals motivate them. Every Faberist believes that if things were just "run the right way," everything would work out, and the City could be paradise. Unsurprisingly, most Faberists come from the lower classes, who have the most to be dissatisfied about.
Twist: Unlike most revolutionaries in the real world, the Faberists are more concerned with theory and political protest than violent action. Terrorist actions are few and far between, and mostly represent splinter groups rather than the faction as a whole. Perhaps that's not a coincidence -- maybe there is a cabal of high-level Faberists who actually want to keep the City as it is, and guide their revolutionary-minded brethren into small-scale and ultimately futile gestures in an attempt to keep them quiet and too busy to actually smash the state. Hm. Not sure if I like that or not -- it kind of makes the whole society a lie -- but it is interesting. I shall ponder...
Next time, we examine the charitable Publicans! See you then!