So if we make cities independent, and they actively go about improving things, what insures that the people that live there benefit and don't have to move down to South Carolina just to find work, while meanwhile, people from all over the country move to that city to take the place of the local workforce, many of whom end up homeless in their, albeit independent and thriving, home town.
An argument then is to be made that you must prevent free movement of people across local boundaries to make this work.
A corollary is that when your local city does all sorts of things to improve the local life, the businesses rather than sourcing locally, source from other cities across the nation, and so on, and local funds flow out, impoverishing the local economy and the very businesses doing this, and return as capital ownership by the, now rather unified (no need to discuss independently billionaires and multinational corporations as the issue anymore) one world economy.
So your cities need not just land value taxes, but tariffs.