Agreed - As far as I'm concerned it's a logical requirement of the analytical model from which AnCaps derive principles of ownership. I agree it's extreme and perhaps even absurd, but if someone is trying to create a defensible model of how to organize the world it should be able to account for all states of the world. Otherwise it's just as extreme and absurd to say there's a fundamental principle called self-ownership. I can sympathize that it is practically difficult to see each state-change that could take us to this extreme, but if people are wanting to think through something more "real world," then they can investigate whether this endgame is really much different than where we might end up as we continue down the path of growing wealth and information inequality.
In my view, we're in one of the best positions in history to map out and coordinate relationships between people, ideas, and objects. If we can identify better ways of handling those relationships and build the infrastructure to support them (and we want to back that mission with some defensible philosophy), then we'd probably be better served re-visiting a lot of these "fundamental" principles to see if there isn't something more fundamental we can explain and solve for. Self-ownership doesn't get us there.