In a world where more and more jobs can be performed remotely with equal verve and success from the home, and where productivity is increasingly an intellectual endeavor rather than an industrial one - the utility of large cities may rightfully be called into question.
Descendants of the walled towns of yore (long obsoleted by the existence of modern artillery), the modern city of today is a product of the industrial age - where for efficiency, large quantities of individuals and raw materials would be located at a major center of cargo lines such that goods might efficiently be manufactured and shipped out to wholesalers and retail locations, and ultimately consumers.
Movers and shakes of industry and government would gather where they might personally inspect and supervise their works, and hangers on (lawyers, judges, hoteliers, restaurateurs) would in turn gather to support the workers and the titans of commerce and government (at a tidy little profit).
When a product travels over a fiber optic cable at the speed of light, a phone or conference call brings folks together from the world over, and when products and goods are delivered with increasing efficiency in the real world...the need to concentrate large numbers of individuals in ant-like hives diminishes.
Given that, historically, the larger the number of people per square mile in a given region the greater the amount of misbehavior per capita (and as a corollary, the greater the amount of expensive effort to deter/suppress/punish said bad behavior) - this is a good thing.
Population density would appear to be inversely proportional to quality of life, and as it becomes less necessary to sustain a modern lifestyle we must reconsider whether promoting greater density is a good and worthwhile project.