Black Lives Matter, the slogan of the movement that began in earnest after the police shooting of Michael Brown in Ferguson, Mo., is a lie.

Taken at face value, the phrase is a truism, since obviously all lives matter. But the people who use it as a shibboleth don’t care about black lives per se so much as scoring points against the police.

When there is some awful tragedy involving a cop shooting or harming a young black man (sometimes justifiably, sometimes not), they muster every ounce of their moral dudgeon and stage demonstrations eagerly covered by a sympathetic media.

Baltimore was an obsession of the Black Lives Matter crowd and of the news media after the death of Freddie Gray from a terrible injury suffered in police custody.

But now that 35 people have been murdered in the month of May, the highest in a month since 1999, the response has been muted.

A few Baltimore organizations are staging anti­violence protests, but they won’t command major media attention. There have been headlines and TV reports about the killing spree, but not ubiquitous calls for yet another national “conversation.”

Let’s be honest: Some black lives really don’t matter. If you are a young black man shot in the head by another young black man, almost certainly no one will know your name.

Al Sharpton won’t come rushing to your family’s side with cameras in tow. MSNBC won’t discuss the significance of your death. No one will protest, or even riot, for you.

You are a statistic, not a cause.

Just another dead black kid, politically useless to progressives and the media, therefore all but invisible.

The same Memorial Day weekend when nine mostly young people were murdered in Baltimore, demonstrators were out in force — not to protest the violence, of course, but the state of Maryland funding a youth jail in a city that rather desperately needs a youth jail.

Just as the Freddie Gray unrest was initially stoked by an inadequate police response, the wave of shootings has been enabled by less aggressive police patrols.

According to The Baltimore Sun, arrests have dropped by about half in May. The implication is clear: More people need to be arrested in Baltimore, not fewer.

And more need to be jailed.

If black lives truly matter, Baltimore needs more and better policing and incarceration to prevent a lawless few from spreading mayhem and death.

Why have the police pulled back? Baltimore’s police commissioner, according to the Sun, has said that in West Baltimore “officers have been routinely surrounded by dozens of people, video cameras and hostility while performing basic police work.”

Daniel Webster of the Johns Hopkins Center for Gun Policy and Research told Vice News that he thinks the rioting carried its own toxic message of disrespect for the law.

Meanwhile, anonymous police officers say they feel that city authorities don’t have their back, understandably enough when Baltimore City State’s Attorney Marilyn Mosby rushed to announce charges against the Freddie Gray officers to placate the mob.

It is wrong for the police to shrink from doing their job, but the past month in Baltimore shows how important that job is. This is especially true in dangerous, overwhelmingly black neighborhoods.

They need disproportionate police attention, even if that attention is easily mischaracterized as racism.

The alternative is a deadly chaos that destroys and blights the lives of poor blacks.

It is a paradox that a figure who is anathema to the Black Lives Matter movement, Rudy Giuliani, saved more black lives than any of his critics ever will.

He did it by getting the police to establish and maintain basic order and defending the cops when the likes of Al Sharpton maligned them.

Now that Mayor de Blasio has pulled back, shootings are trending up in New York City. But it’s OK, as long as nameless young black men are the ones being shot at.

For progressives, only some black lives matter.