Jeremy Corbyn’s problem is not, as some in the Labour party are arguing, that he is too leftwing to get elected, but that he is not leftwing enough. That is, if we define leftwing as “identifying the problems of the nation (and the world) as they are, rather than as we wish them to be, and positing solutions that belong to the future and not to the seventies”.

Unfortunately, nobody does define leftwing like that; instead, in the context of this debate, it means “person similar to myself, only without my grip on reality and reason”. It is salient that this debate has never, in the history of university mini-debating chambers, parliament, saloon bars or golf, happened on the right. They call one another cruel, swivel-eyed, wet, heartless – there is no shortage of animus there. Yet they have identified this fundamental point: that when you take your own worldview and apply degrees of it as an insult to people who, with points of difference, broadly share it, outsiders regard you as they would two siblings fighting in a car. They don’t care who’s right so long as they don’t have to get into the car.

So anyway, that’s always been my line: if we absolutely must have this conversation, first, I think we should do it in private, by email. Second, because, in a world where Chuka Umunna can describe some of those claiming social security as “people who can work but refuse to work”, and Iain Duncan Smith resigns because his prime minister’s reforms are too extreme for him, the centre has moved so far, so fast, that to try to map the reach of its wings is like trying to take a photo of a cat falling down the back of a sofa on an iPhone.

On Saturday, at the Cambridge literary festival, I realised why this debate couldn’t be won and what it was really about. “Look at this audience,” said David Aaronovitch (I’m paraphrasing a bit, but not unfairly). “You already support Labour. You’re not the people we need to be persuading.”

“We don’t need to persuade the people of Highgate and Cambridge,” said a local councillor, who claimed later that he intended to spend the following day leafleting from seven in the morning until nightfall, because he – the true Labour loyalist – was interested in the people who didn’t think about politics, who weren’t in a debate at the weekend, and who couldn’t afford to go to literary festivals.

The phrase “virtue signalling” came up a lot, which is the sequel insult to “champagne socialist”; again, it doesn’t have very much meaning, beyond “person X holds views less compromised and more ambitious than mine, ergo, person X is a narcissist who uses other people’s misery as grist to their own self-fashioning.” It was invented by the mild-mannered rightwing polemicist James Bartholomew.

If you can take your opponent’s core belief, the engine of their argument, and use it as proof not that they’re wrong but that everything they say is just opportunistic self-aggrandisement, by God, that’s undermining. If you can appreciate the elegance in a cynical discursive manoeuvre, it’s almost beautiful.

Critically, if you are too rich and insufficiently diverse, if you are too old (“baby boomers” has now, bizarrely,become an insult of its own), or too young (by definition, hysterical and with no understanding of the history of compromise that has made the Labour party great), you aren’t representative and therefore your beliefs are wildly separate from those of the mainstream, the great mass of the unengaged, who must be awoken if Labour are ever again to govern.

By definition, if you are politically active but not in the high command of the parliamentary Labour party, then you are an aberration whose involvement doesn’t just distract the opposition from its proper purpose but actively derails it. There is no point in the party unless it can win, and cranks prevent its winning. The fact that even before the cranks came rushing in it didn’t know how to win is skated over with a hand-waving, “nobody trusted us on the economy”.

The idea that there is a solid mass of people whose views don’t change, who all agree, who cannot be persuaded, and who just need exactly the right bespoke package of policies to meet their needs and someone to deliver it, by leaflet at 7am on a Sunday morning, is accepted without question. The only people who matter are the alienated; the way to engage them is hard graft, a flesh army delivering leaflet after leaflet, never wondering why the Tories don’t bother and leave that to mass mail-outs; there is no point having an idea without the power to enact it, so clearly, this is no time for an ideological discussion.

In short, this division has nothing to do with the left or the right, the extremists or the moderates. It is about whether or not we’re allowed to engage, democratically, or whether it is better to leave power to the professionals, the self-appointed conductors of the Clapham omnibus.

The charge is: you are too rich to take a view; you are too privileged to take a stand. And the rebuttal is: I may be doing all right in this world, but I want to live in a better one.