What would you do if you were the mayor of Detroit? Right now entrepreneurial urbanists in Detroit and other rust belt cities are by necessity re-envisioning their urban milieus, trying to make them greener, more creative, more prosperous places. There are pockets of success here and there, but the scary part is that all of this re-imagining might not matter. Given the rate of industrial decline, it would seem that distant global forces are shaping urban landscapes in ways that are as stoppable for urban planners as the weather.

The late management expert Peter F. Drucker wrote a piece in Foreign Affairs called “The Changed World Economy” in 1986 that accurately foresaw the problems that cities are dealing with today. The manufacturing sector, he said, was becoming decoupled from blue collar employment. America may produce just as much, but it’s doing so with fewer workers. At the same time, he saw flows of global capital—investment money moving from one place to another—as replacing in importance the actual physical trade in goods. Put together, this means that job opportunities come and go, moving around the country (and globe) at unprecedented speed. I’m worried that this accelerated mobility of opportunity might be too much for most people to keep up with.

The real problem in the ever-mercurial global economy is how to manage cities whose roles in it could become unmarketable by next week. The urban theorist Richard Florida argued in the March Atlantic that the answer was to redesign our urban geography for increased mobility. That way people can keep up with changing job markets and members of Florida’s lionized “creative class” of white-collar professionals can find one another. The old system that encouraged home ownership should be jettisoned in favor of renting, which makes it easier for people to pick up and move without the time consuming agony of home selling. Cities should be more concentrated, less suburban, and more connected by public transit. I’m generally fine with those propositions, as are most urban planners. However, there are bigger issues at hand when we talk about enhancing mobility to accommodate the volatility of unleashed markets.

The inefficient suburban-centric development model of the past few decades isn’t the only reason why migration is so hard. When people migrate nationally or internationally for the (potentially false) promise of a better life, they leave behind important familial and communitarian networks of social support. Permanent communities become temporary residences of job seekers en route from one place to the next, and any sense of connection to place is lost. Relationships fall under strain as families separate out of necessity. So the system of creative capitalism can be painfully atomizing.

There are also brutal legal barriers that prevent mobility. While goods and capital can move between cities freely (and job opportunities with them), millions of people around the world have to keep their very presence a secret in order to avoid deportation or Byzantine detention. It’s ironic that, in the age of NAFTA, the governments of the U.S., Mexico and Canada are spending billions on high-tech surveillance to regulate who travels among them. In China’s coastal cities—the geographic centers of the country’s economic activity—rural migrants are a legally mandated underclass.

Finally, not everyone can afford to move and the poorest are left behind amidst urban blight and neglect. What do we do about the immobile? What do we do with cities that are net losers of the “creative class”? For this so-called creative brand of capitalism, the uncreative are someone else’s problem. As Florida says, “We need to be clear that ultimately, we can’t stop the decline of some places, and that we would be foolish to try.” I would say that this is not at all clear. There is an inherent inhumanity in leaving people and their cities in the dust. Besides, the cost of finding ways to get so-called obsolete classes of workers gainfully employed where they live is looking preferable to the social costs of managing huge ghost cities and permanent spatial inequality.