It used to be possible to argue that people were overplaying the concern that social media is fundamentally changing political debate. Yes, it enables a few oddballs with some funny ideas to find each other online and create pressure groups advocating bizarre changes in the law. The U.S. Association of Reptile Keepers speaks for itself, but otherwise, what does it really change? Rallies and protests, after all, are not so different from mass “Twitter wars”, and even before instant communication became ubiquitous, the public was very good at mass organisation when it wanted to defy the Government.

But today’s Momentum propaganda video has made me rethink. The clip, which has been viewed and retweeted tens of thousands of times, depicts a group of out of touch middle aged people with plummy voices sitting around drinking wine and laughing at young “gullible” people who vote for Jeremy Corbyn. The short film is punchy propaganda but it represents everything that’s wrong with social media politics.

For a start, it brazenly encourages class warfare. The heartless, hypocrites in the video are white, middle-aged and middle class. The stereotyping, the “us-and-theming”, is shameless and would never be allowed in mainstream media. We laugh at the clunky political correctness in our TV shows, but the fact that ITV, BBC and Channel 4 all painstakingly attempt to avoid stereotypes when possible says something good about the state of modern broadcasting. The “baddies” on mainstream media come from a range of social demographics. In a Momentum Twitter video, though, the message is clear: the baddy is The Other. White, middle-aged, middle-class people aren’t like us, they don’t understand you, their world-view is wrong, and they need to be stopped.

It is also designed to stoke up resentment between the generations. The vast majority of Jeremy Corbyn’s supporters are middle class young people with parents who look and sound very like the people in the video. These young people have justifiable grievances. They are in debt; they can’t hope to get on the housing ladder; and their extraordinarily expensive degrees aren’t getting them the jobs they want.

But instead of providing answers, far-left Momentum weaponises these grievances with the sole aim of turning children against their parents.

Before social media, a successful political campaign would generally appeal to as many ages as possible – now, the more it is divisive the better. The idea seems to be to mobilise young people in a place their parents can’t reach, to stir up righteous fury, and to create an army to bring down the old folk who “just don’t get it”. What “it” is is never made clear, but if you’re one of us, the implication is, you’ll understand.

The video, like everything else on Twitter, also manages to flatten political debate into something two-dimensional. Traditional political debate addresses a problem by seeking to answer the what, the when, the why and the how. Twitter political debate stops at the what. When Momentum has recognised the existence of a grievance, that’s the job done. With only 140 characters, or a two-minute video, there’s no room to address how and when Jeremy Corbyn is going to “deal with” student debt or even whether he should. To create an army of students, it is enough to point out that he has recognised that students are upset because they are in debt. Well no shit Sherlock.

If Momentum’s vile video teaches us anything, it’s that we cannot keep pretending that social media is just a new platform for old debates. The toxic messaging which has become Momentum’s speciality could only thrive in a post-truth world where claims need no evidence, arguments need no scrutiny, and adults are nowhere to be found – and, in Twitter, it’s found that world.