This should not even need saying, but obviously, it does. So, for the record:

To oppose police brutality is not to oppose police. No one with a brain stands against police when they do the dangerous and often-dirty job of safeguarding life and property. But no one with a conscience should stand for them when they assault or kill some unarmed, unthreatening somebody under color of authority.

Support good cops, oppose bad ones: You’d think that a self-evident imperative. But it turns out some of us are unwilling to make the distinction. For them, the valor of the good cops renders the bad cops immune to criticism.

As you’ve no doubt heard, an unstable man named Ismaaiyl Brinsley went cop hunting in Brooklyn on Dec. 20. He randomly shot to death two police officers, Rafael Ramos and Wenjian Liu, in retaliation for the unpunished police killings of two unarmed African-American men in Ferguson, Missouri, and Staten Island.

What followed was tiresomely predictable. Erick Erickson of Fox “News” said President Obama and New York Mayor Bill de Blasio had “all but encouraged retaliation” against police. Rudy Giuliani accused the president and the mayor of putting forth propaganda that “everybody should hate the police.” The National Review Online blamed Obama and de Blasio for creating a “racially-charged, rabidly anti-police” atmosphere.

It might be hard to tell from that superheated rhetoric, but the sin they refer to is as follows: Obama and de Blasio called for reform as people vigorously protested the Staten Island and Ferguson killings.

Tempting and easy as it might be to deconstruct all that right-wing drivel, what should truly trouble us is the behavior of the police in the wake of the shooting. Meaning those New York cops who pointedly turned their backs on the mayor as he spoke at Ramos’ and Liu’s funerals. The NYPD has also engaged in a work slowdown — arrests, tickets and summonses down sharply over the last two weeks.

With this temper tantrum, this turning its back on the representative of the people it serves, the NYPD shames itself, shames its profession, and dishonors the memory of its slain men. It also, paradoxically, makes stronger the case for reform.

What other profession behaves this way? Do good lawyers see an attack on bad lawyers as an attack on them all? Are good firefighters threatened by criticism of incompetent ones? Yet this behavior is routine among police — something to keep in mind when we talk reform.

It’s all well and good to say we need body cams, but that’s just a start. As the cases of Rodney King in Los Angeles and Eric Garner in Staten Island make apparent, a visual record is useless if people are unwilling to see what is right in front of them. And yes, there should also be some state-level mechanism for a special prosecutor in cases like these, so we are never again asked to believe impartial justice can be meted out to a given cop by people in the local courthouse who work with him every day.

But the behavior of New York cops, their righteous pique at the idea of being questioned by the people they work for, suggests another needed reform. We must find ways to change police culture so that it becomes easier for police themselves to police themselves, to name and shame the brutal or trigger-happy incompetents among them.

Yes, that will be much easier said than done: In no other job might your life depend tomorrow on the colleague you stand up against today. But the alternative is this status quo wherein police are effectively above the law they swear to uphold.

Where bad cops cannot be questioned, good cops cannot be trusted — and all cops are undermined.

There’s something else that should not need saying, but does.

Leonard Pitts Jr. is a columnist for the Miami Herald. Readers may write to him via email at: lpitts@miamiherald.com.