As disturbing as it is to watch that video of a black protester being beaten and dragged out of a Donald Trump speech in Alabama on Saturday, you should watch it. Everybody should, if only for the clarity that it brings to a phrase that’s been hampering public discourse about racism in America for the past two years : “all lives matter”.

The important part starts around the one-minute mark of the original video, when the protester is pulled up off the floor and led away by members of the event security staff and some of the more aggressive volunteers from the crowd. The man is wearing a T-shirt bearing the slogan “Black Lives Matter”. At least one Trump supporter standing near the video camera starts chanting a refutation: “All lives matter.”

It’s valuable to see images of a black man being shoved and pushed and jeered and taunted to the soundtrack of these words. In 2015, in America, those three words, “all lives matter”, are a racist slogan. Any other interpretation is wrong.

Language does not happen in a vacuum. Words and phrases bounce off of other words and phrases. Context gives them meaning. This is the only way verbal communication works.

The phrase “black lives matter” – the phrase mirrored, distorted, refuted and mocked by the phrase “all lives matter” – entered the lexicon in 2013, after 28-year-old neighborhood watchman George Zimmerman was acquitted for the shooting death of unarmed 17-year-old Trayvon Martin in a gated housing community in Florida.

The choice of words was meant to address a horrible disparity in this country: black people in America are nearly eight times more likely to die of homicide than white people.

At its root, the phrase is a call for the US Justice Department to change this – with the implied suggestion that more effective prosecution of people who kill unarmed black teenagers would be a good place to start.

President Obama put it well during a panel discussion about the criminal justice system last month. “I think the reason that the organizers used the phrase ‘black lives matter’ was not because they were suggesting nobody else’s lives matter. What they were suggesting was, there is a specific problem that is happening in the African American community that’s not happening in other communities. And that is a legitimate issue that we’ve got to address.”

Since then, though, as a response to the Black Lives Matter movement, the words “all lives matter” has become a commonly heard refrain. And the tension between “black lives matter” and “all lives matter” has become an issue on both sides of the current presidential campaign, with various candidates stumbling over the subject at various times.

Often people who say “all lives matter” say it pointedly, correctively under the veneer of the idea that “all men are created equal”. It is meant to refute the idea that “only” black lives matter.

But understanding “black lives matter” to mean “only” black lives matter has been a misinterpretation from the beginning, one made in ignorance of the intent of the statement and the statistical facts that led to it. It’s often a misinterpretation made in innocent ignorance, I’m sure. I would argue that it is more often made in craven, self-pitying defensiveness, in protection of an unfair status quo in our country that people like those chanting in support of Donald Trump’s campaign for president hope to maintain.

Watch the clip again. Listen to the chant “All lives matter! All lives matter!” Hear how it sounds. See it juxtaposed with the images of a crowd of white people swarming, pushing, shoving a black person, celebrating as he’s led away. “Get him out of here,” someone says. “Get your ass out of here!”

If you choose to say those words “all lives matter” in a conversation with your friends, or if you type the hashtag on Twitter or put it up on Facebook or something, you should know what you’re saying. You are not saying that all human life is equal. You are saying that there is no racial disparity in America. You are refuting rafts of statistics that prove there is racial disparity in America. You are saying, simply and straightforwardly, that black lives do not matter. At least not as much as white ones do. Is this what you want to be saying?