The Post, which enthusiastically championed the NYPD during this year's turmoil, portrayed this slowdown in near-apocalyptic terms—an early headline for the article above even read "Crime wave engulfs New York following execution of cops." But the police union's phrasing—officers shouldn't make arrests "unless absolutely necessary"—begs the question: How many unnecessary arrests was the NYPD making before now?

Policing quality doesn't necessarily increase with policing quantity, as New York's experience with stop-and-frisk demonstrated. Former Mayor Michael Bloomberg asserted that the controversial tactic of warrantless street searches "keeps New York City safe." De Blasio ended the program soon after succeeding him, citing its discriminatory impact on black and Hispanic residents. Stop-and-frisk incidents plunged from 685,724 stops in 2011 to just 38,456 in the first three-quarters of 2014 as a result. If stop-and-frisk had caused the ongoing decline in New York's crime rate, its near-absence would logically halt or even reverse that trend. But the city seems to be doing just fine without it: Crime rates are currently at two-decade lows, with homicide down 7 percent and robberies down 14 percent since 2013.

The slowdown also challenges the fundamental tenets of broken-windows policing, a controversial strategy championed by NYPD Commissioner Bill Bratton. According to the theory, which first came to prominence in a 1982 article in The Atlantic, "quality-of-life" crimes like vandalism and vagrancy help normalize criminal behavior in neighborhoods and precede more violent offenses. Tackling these low-level offenses therefore helps prevent future ones. The theory's critics dispute its effectiveness and contend that broken-windows policing simply criminalizes the young, the poor, and the homeless.

Public drinking and urination may be unseemly, but they're hardly threats to life, liberty, or public order. (The Post also noted a decline in drug arrests, but their comparison of 2013 and 2014 rates is misleading. The mayor's office announced in November that police would stop making arrests for low-level marijuana possession and issue tickets instead. Even before the slowdown began, marijuana-related arrests had declined by 61 percent.) If the NYPD can safely cut arrests by two-thirds, why haven't they done it before?

The human implications of this question are immense. Fewer arrests for minor crimes logically means fewer people behind bars for minor crimes. Poorer would-be defendants benefit the most; three-quarters of those sitting in New York jails are only there because they can't afford bail. Fewer New Yorkers will also be sent to Rikers Island, where endemic brutality against inmates has led to resignations, arrests, and an imminent federal civil-rights intervention over the past six months. A brush with the American criminal-justice system can be toxic for someone's socioeconomic and physical health.