President Barack Obama and New York Mayor Bill de Blasio publicly asked that the funeral of fallen NYPD officer Rafael Ramos be a politics-free event. They were begging the question, of course: any issue specifically raised by both the president and the mayor is de facto politicized by virtue of such mention alone. Ramos's death — he was one of two cops killed in a Brooklyn ambush — was unavoidably situated in this mercurial political moment surrounding police violence and counter-violence against cops. Apolitical was never an option.

A strange point of unwitting agreement then emerged between protesters and police. Protesters refused to pause their politics around the funeral. Marches continued, hundreds strong in New York and beyond, and a "die-in" was staged in Grand Central station the day after de Blasio asked that they be halted. A sizable contingent of the NYPD performed its own act of political demonstration: Several hundred cops turned their backs on the mayor as he spoke during the funeral service for Ramos, a renewed and spectacular assertion of the view, amplified by New York's largest police union, that the city was attacking its cops. The protesters wouldn't stop or pause, and nor would the police. But one of these acts of defiance was far more dangerous than the other.

The individuals who continued to protest ahead of Ramos's funeral were acting against claims that such demonstrations problematically disrespected the deceased officers' mourners. As I wrote at the time, it was right that a protest movement struggling for more than an end to police impunity, but nothing short of demanding that black life be valued in this country, not be derailed by the actions of one revenge-fueled gunman.

The NYPD officers who turned their back arguably did a more spectacular job of derailing the funeral service from commemorating Officer Ramos and politicizing the event. But the signification of the act is troubling, and goes beyond disrespecting De Blasio. These cops, under the auspices of their powerful union, showed with their bodies what they do in the face of even moderate criticism: They turn their backs. It is without question criticism of the NYPD that they were acting out against — specifically mild and reasoned criticism from a mayor, who has also been careful to heap praise on the force, too.

Police commissioner Bill Bratton and former mayor and NYPD enthusiast Rudi Giuliani only deemed the cops' display "inappropriate." This was more than a violation of decorum, though: hundreds of officers, led by their representatives, brazenly dissenting from a reasonably and moderately critical city leader is a worrying display of intransigence and belief in their own unassailable moral stance. It is a message from behind the thin blue line that those hoping to see serious change in New York policing and beyond should take to heart. In the face of disruptive popular protests after numerous police killings of unarmed black men and teens, in disregard of studies showing racist patterns of police harassment and arrests, politicians have finally responded this year to say that something must change. But what hope remains for effective reform, let alone structural change, when in the face of reasoned criticism, police dig in their heels, claim they are under "attack" and, quite literally, turn their backs? It is the behavior of a bully, tongue out and fingers in ears when reprimanded. But this bully is an armed force.

If police impunity accorded by the legal system is a problem, then the fraternal culture of reactionary defensiveness is a corollary obstacle to anything like justice. Consider all the police in Ferguson and elsewhere donning "I am Darren Wilson" in support of Mike Brown's killer. This is frightening, because a force resistant to criticism is immune to change. This is the challenge that efforts to end police brutality face; banging heads against a blue wall. If police officers cannot see how they are read as a force for violence in many communities, then they can only act as enemies to those calling for an end to police violence; cops cannot end a brutality they do not, or will not, see. Even the slightest comprehension that De Blasio's very tepid calls for police reform may have some basis would have stopped an officer turning his or her back at that funeral. But hundreds displayed no such comprehension at all.