Once well underground, you know exactly where you are. Nothing can happen to you, and nothing can get at you. You're entirely your own master and you don't have to consult anybody or mind what they say. Things go on all the same overhead, and you let 'em, and don't bother about 'em. When you want to, up you go, and there the things are, waiting for you.
Squatters. The dispossessed. The water rats. Denizens of the deep, citizens of the shallows. And a lot of them were interested in trying something different, including which authorities they gave their consent to be governed by.