Graeme Archer is a statistician and a former winner of the Orwell Prize for Political Blogging.

It’s easy to laugh at Yassmin Abdel-Magied’s reaction to a talk by the novelist Lionel Shriver.  (Abdel-Magiedis is an Australian engineer and commentator, and also a sometime Guardian contributor, whose TedX talk has been watched millions of times.)   As the writer of We Need To Talk About Kevin gave her speech on “Community and Belonging” at a festival for writers in Brisbane, Ms Abdel-Magied’s emotions went into hyper-drive.

“Mama, I can’t sit here,” I said, the corners of my mouth dragging downwards. “I cannot legitimise this …”

So Yasmin walked out on Lionel:

“As my heels thudded against the grey plastic of the flooring, harmonising with the beat of the adrenaline pumping through my veins, my mind was blank save for one question.“How is this happening?”

How indeed? What had Shriver done to cause Abdel-Magied to flee, her mind (almost) completely blank? Something vile, surely.

Shriver was, in fact, merely discussing identity politics, and its baleful influence on fictional practice; she attacked the absurd notion of “cultural appropriation”: the idea that “trying on other people’s hats, stepping into their shoes” – the entire point of writing fiction – is nothing more than “wearing the teeth of your pillaged enemy as a necklace”.

(This description, which I’ve purloined from Libby Purves’ excellent column on the subject, appears in Time, and is about – I’m not making this up – which hairstyles are permissible for different ethnicities to possess.)

What makes my own mouth drag downwards – what I can no longer “legitimise” – is the idea that simply laughing at people like Abdel-Magied is enough. (I hope to God that neither she nor her mother ever pick up a copy of Animal Farm. Appropriation of animal culture, and the villains are, oh God, pigs.)

Though it’s hard, not laughing at identity politics. Those (white) Black Lives Matter idiots who jerked around on a hot City Airport tarmac were themselves accused of “cultural appropriation” (because, presumably, only black people can protest about the “racism” of runways and aircraft noise, because… no; me neither. Left-wing activism, devouring itself.)

But titter ye not. Identity politics is doing serious harm to the chances for a good society; that is, one which is comfortable with itself and its individual members. (What a policy wonk might call “cohesion”.)

As Shriver put it in her speech:

“Those who embrace a vast range of “identities” – ethnicities, nationalities, races, sexual and gender categories, classes of economic under-privilege and disability – are now encouraged to be possessive of their experience and to regard other peoples’ attempts to participate in their lives and traditions, either actively or imaginatively, as a form of theft.”

Identity politics in literature is bad enough. What’s worse is that it’s taking hold of a growing segment of the British Left, desperate to fill its post-Blair not-socialist gap. Here is how it works.

First, ignore the (observable) fact that every human being alive is in possession of a near-as-dammit infinite number of overlapping identities (list your own, then stop when you run out of patience.)

Secondly, and ignoring this inconvenient fact, insist that every human can be deconvolved into a finite number of different categories, by applying some sort of sociological Fourier transform. (Graeme is 50 per cent gay and 15 per cent Tory and five per cent vegetarian and so on.)

Thirdly – and here is where we move from the realm of sociological guff, and start harming ourselves – construct a mainstream politics which prioritises these (fictional – the irony!) mono-identities, and devises policies specific for each one’s “needs”. A politics of “communities”, by definition plural, by definition non-overlapping.

Politics is about choosing, so a ranking of the identities, and their various intersections, must be imposed. Gay > Straight, for example, but Left-Straight > Tory-Gay, which explains why straight Labour activists can’t see that turning up at Pride marches wearing “Never kissed a Tory” teeshirts is a moral obscenity: their place in the hegemony – the rank of their primary identity – vis-a-vis Tories excuses it.

This isn’t uniquely a Left-wing pathology. There is a spectre of a mote in a type of Right-wing eye too; that’s why Andrea Leadsom thought it fine to do all that “As a mother” thing: picking a single aspect of her identity and using it to rank the leadership potential of everyone else on the planet. Mothers > Non-mothers.

Such a politics goes wrong because we are not “deconvolvable”. We are convoluted, by design and by our enormous good luck.

We don’t live in the frequency domain, where I’m “50 per cent gay, 20 per cent Scottish, 10 per cent Tory”, and so on. I am 100 per cent all of these things – and a near infinite number more such things – all at the same time.

A politics which pretends otherwise is doomed to failure, not least because (have you noticed?) it discourages empathy: not-You is not only unknowable, either in literature, or in political discourse; not-You is forbidden, because You > not-You.

At best, identity politics produces earnest young women like Abdel-Magied, who waste their intellectual potential by finding other gifted women to be angry about. Over nothing, Yasmin. You stormed out over nothing.

At the mid-point of the scale, it gives us Ken Livingstone, who knew perfectly well what he was doing when he embraced Qaradawi or drivelled on about Hitler. Indeed, the thought that should make your blood run cold isn’t really what he said or did. It is that, from the perspective of an identity politician, Livingstone was being entirely rational: there are more Islamic voters than Jewish or gay ones, and that reductive frequency-dimensionality is the only world Livingstone inhabits. Islam > Jew/gay.

At its worst, of course, identity politics gives us Rotherham, and Tower Hamlets, Trojan Horse schooling and gender-segregated Labour Party meetings. It gives us the murders of Asad Shah and Jalal Uddin.

And because working-class people – those who didn’t get to grammar school – can be clumsy, sometimes, in the way they express concern about immigration, identity politics provided an easy way for middle-class liberals to avoid even having to think about the topic. Racists. (There is a sign that – Brexit, Trump – liberals are starting to wake up to the limitation of their approach.)

How to fight this? First, recognise that words matter; words are both the weapons in this war and the bricks to build something better. I’ve just spent a year in the Department For Communities & Local Government. Good people, wrong name. We need a Department Of Community, not “For Communities”, and we need a politics, not of identity, but of values.

Had we a politics of values, for example, universities could stop tying themselves in knots, defending the campus presence of groups inimical to freedom. “The entire point of a university is intellectual rigour and freedom, so if your society is opposed to those values, then sorry: no room at this inn.” That isn’t a contradiction. It’s rejecting the calculus of identity politics. Our values: Freedom > Non-freedom, regardless of your “identity”.

You can have identity politics, or you can have a good – cohesive – society. You certainly cannot have both.

Imagine being Abdel-Magied. Seriously: imagine it. Put yourself in her shoes, inhabit the persona of someone who could walk out on Lionel Shriver and feel brave to do so. Breathe in an understanding of where politics is going so very, very wrong.

Abdel-Magied might describe such empathetic engagement as “cultural appropriation”. I would call it absolutely vital, and absolutely just the first step in unwinding the intellectual noose of identity politics from around our political necks.