Outrage over new development often coalesces around extra-tall skyscrapers, but the ordinary is far more corrosive. The pair of 30-story-plus towers facing each other across Broadway at 99th Street galvanized the neighborhood into demanding new regulations limiting the height of future buildings. The result is a pleasing lone spike in the skyline—and rules that ensure it will remain thus. But below 96th Street, Broadway’s serrated profile is being evened out. What will replace the low, old blocks is not a glittering chain of architectural marvels, but a series of blocky buildings that rise 150 feet and then set back at the top. They can be lavished with nostalgic detail, as at the new Laureate, at 76th Street, or they can be perfunctorily designed. Either way, zoning dictates their bulk and form, turning the avenue into a corridor of near-total uniformity.

It doesn’t have to be this way. Planners could develop more sophisticated zoning tools to foment commercial diversity and architectural variety: They might, for instance, require new stores with more than 50 feet of frontage to be spaced two or three blocks apart. That will happen only if neighbors demand it. The only people who can curb the blight of sameness are the ones who suffer the consequences.

The architect and provocateur Rem Koolhaas recently suggested, in a polemical exhibit called “Cronocaos,” that the world should routinely clear out the underbrush of obsolete junk architecture. Preservationism, he argued, is keeping cities sluggish and out of date. Koolhaas was once a connoisseur of New York’s contradictory quirks; these days, he has only to stroll up Broadway on the Upper West Side to observe the baleful outcome of the progressive erasure he advocates. Here, the preservationist impulse is needed not in order to cherish the past, but to safeguard the vibrant present.

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• Archive: “Architecture”
• Articles by Justin Davidson