Right now, if you use Facebook, Facebook owns you. If you don't use Facebook but all your friends do, Facebook still owns you, but you're worthless to it, and it punishes you for failing to generate value by making you as close to socially invisible as it can - which is pretty damn close. (Ask me how I know!) None of this is deliberate, in the sense of an evil conspiracy cooked up by cackling villains. But all of it is true.
The purpose of Urbit is to make it possible for people to own themselves. Doing so is not free of charge. (Should it be? Are you worth nothing?) But it is, or will be once (if) it's possible at all, as cheap as can be made practical - which is very cheap indeed, or free, if you don't mind opting out of guaranteed and durable identity. The tradeoff is that people who don't opt out may not be as quick to trust people who do. But that's a choice you get to make, instead of, as now, a choice that Facebook makes for you. I can't speak for anyone else (especially Tlön), but I've had enough of Facebook making choices for me. Have you?