Police unions do have critics on the right. But thanks to a mix of cultural affinity, conservative support for law-and-order policies and police union support for Republican politicians, there hasn’t been a strong right-of-center constituency for taking on their privileges. Instead, many Republican governors have deliberately exempted police unions from collective-bargaining reforms — and one who didn’t, John Kasich of Ohio, saw those reforms defeated.

In an irony typical of politics, then, the right’s intellectual critique of public-sector unions is illustrated by the ease with which police unions have bridled and ridden actual right-wing politicians. Which in turn has left those unions in a politically enviable position, insulated from any real pressure to reform.

Yet reform is what they need. There are many similarities between police officers and teachers: Both belong to professions filled with heroic and dedicated public servants, and both enjoy deep reservoirs of public sympathy as a result. But in both professions, unions have consistently exploited that sympathy to protect failed policies and incompetent personnel.

With this important difference, however: Even with the worst teacher, the effects are diffused across many years and many kids, and it’s hard for just one teacher to do that much damage to any given student. A bad cop, on the other hand, can leave his victim dead or permanently damaged, and under the right circumstances one cop’s bad call — or a group of cops’ habitual thuggishness — can be the spark that leaves a city like Baltimore in flames.