Even as so many crises roiled the world recently, the news that a development on the Upper West Side of Manhattan would proceed with a brand of distasteful social engineering still managed to command international attention. The building, in what is known as Riverside South, a stretch of land reaching below 72nd Street that seems largely like a pop-up location for people who have never heard of Katz’s deli or the G train, had received approval from the city for separate entrances — one for wealthy residents and one for those earning far less who would occupy the project’s affordable units, in a separate wing.

This seemed to provide more evidence that living in Manhattan has become increasingly like a flight to Houston in which one is made to board in Zone 4 and eat only stale pretzels.

The “Upstairs, Downstairs” effect was permissible under a change to zoning codes made during the Bloomberg era that gave developers who provided affordable housing in market-rate projects discretion over these particulars, in addition to the considerable tax breaks they receive. Although the building’s configuration is anathema to the values embraced by the de Blasio administration, forcing the developer to abandon it would involve costly, not entirely tenable litigation, which would slow the progress of the city’s affordable-housing plans, the administration said. The focus now is to reverse the zoning change, Deputy Mayor Alicia Glen told me, a process that should take about a year.

The “poor door,” as it has been called, is an odious response to a problem whose solution is neither obvious nor easily achievable through the mechanisms of policy: How, and to what extent, should the city mandate economic integration? The Riverside development is unusual, and even vaguely radical, in the sense that its luxury units are condominiums rather than rental apartments.