When I was a small child, something called “the suburbs” kept snatching away my friends, like a monster hiding under the bed, but worse. Over time, I’ve come to appreciate why my friends moved. The urban neighborhoods of my Brooklyn youth were a little rough around the edges, and they didn’t offer growing families much in the way of elbow room. I couldn’t fall asleep without the sweet sound of sirens blaring, but not everyone felt the same way. The suburbs have long been a welcome refuge for families looking for a safe, affordable place to live.

But for many Americans, the suburbs have become a trap. This week, Radley Balko of the Washington Post vividly described the many ways bite-sized suburban municipalities in St. Louis County prey on poor people. Towns too small or too starved of sales tax revenue to sustain their own local governments stay afloat by having local law enforcement go trawling for trumped-up traffic violations, the fines for which can be cripplingly expensive, and which only grow more onerous as low-income residents fail to pay them. Those who can afford lawyers know how to massage a big fine into a smaller one. Those who can’t dread their run-ins with local police, who often come across less like civic guardians and more like cash-thirsty pirates. The resentment and distrust that follows is, according to Balko, crucial for understanding the recent unrest in Ferguson, Missouri.

Could it be that the problems plaguing St. Louis County reflect a larger failure of fragmented local government? Would these problems go away if, say, St. Louis simply absorbed all of these petty fiefdoms? I doubt it. The deeper problem is that the low-density suburbs of single-family homes that are common in this part of Missouri, and indeed across the country, are fundamentally inhospitable to those who find themselves at the bottom of the economic ladder.

You might be wondering why poor families are moving to the suburbs in large numbers—the number of suburban poor grew more than twice as quickly as the number of urban poor between 2000 and 2011—if they are such hard places for poor people to get ahead. Part of it is that as middle- and high-income households moved to the suburbs, the low-wage workers who look after their children had little choice but to follow. Then there is the fact that as America’s most productive cities experience a revival, gentrification is displacing low-income families to outlying neighborhoods and towns.