Given the premise that cities have a fundamental advantage, what's the problem? Just wait a bit and liberals in cities will vastly outnumber rural conservatives, no?
This would eventually result in violent revolution. Suppressing that revolution will require a complete forfeit of civil liberties.
There's another reason it's bad too, and it's economic: in this world you will not be able to get ahead. These super-concentrated mega-cities will see runaway real estate inflation due to the "law of rent," while jobs will be scarce elsewhere. The choice will be: move to a "real" city and spend all of your surplus income on rent, or live elsewhere and have no opportunity to advance your career. The urban model looks a lot like the old "company store" model, which is a form of feudalism more or less.
In the end this future looks like a 1980s B-grade cyberpunk dystopia: endless slums and rural wastelands patrolled by drones and special forces officers and dotted by gated totalitarian enclaves for the super-rich. "DNA sample and body scan are required for entry..."
This is the direction we're headed if the cities that are absorbing the economy continue to reject population growth. But there's no reason they can't affordably include a much greater proportion of the population in denser structures.
