And that doesn't even touch the economics: For the most part cities make money by services and not by physical items. Services are very lucrative, so on paper cities make tons of money. But they don't make anything people need to live.

Virtually every single thing people buy in a city comes from outside the city. It's not a lifestyle that everyone can adopt. For the most part there's a balance, with some living in a city and some rural - but people should be extremely cautious about any kind of policy that can mess with that balance.