Culture wars are endless because their participants enjoy them so. It’s fun, if you are on the right, to mock liberal double standards and break liberal taboos. So much fun, it becomes instinctive: a way of lashing out rather than a way of thinking.

If the left is dominated by puritan preachers who denounce the faults of everyone but themselves, the right is dominated by a satirical “contrarian culture”, which is now so predictable there’s nothing contrary about it. Liberals and leftists are humourless hypocrites, the party line runs. At Oxfam or in Hollywood, they satisfy the brute desires they deplore in others. In the privacy of their Tuscan and Hampstead homes they show every indication of wanting to hoard rather than share their wealth. Worst of all they are elitists, who look down their dainty noses at the masses who voted for Brexit and Trump, and damn them as racist fools. The satirical right dominates the conservative web and newspapers because it delivers the occasional truth about liberal hypocrisy, which you do not have to be a conservative to appreciate. Satire worked as a counter-culture protest because from the 1990s until 2016 the “establishment” was politically correct, and most of us enjoy seeing the pomposity of the powerful punctured. As the contrarians head to power, however, outsiders can see the teeth behind the smirk. The label that has stuck to the demagogues who dominate British and American politics is “the alt-right”. But, as Brexit is proving, it is as much a “bullshit right”.

I am not being vulgar but am drawing on the work of Harry G Frankfurt. Unlike liars, who at least know the truth when they deceive, the philosopher explained, bullshitters have no concern for truth. They don’t care if they are lying or not. They just say whatever it takes to win. “By virtue of this,” Frankfurt ruled, “bullshit is a greater enemy of the truth than lies are.”

Truth is not bullshit’s only enemy. The frivolity with which a generation of rightwingers treated politics leaves them without an idea of how to govern when they become the establishment they once despised. Even when they are in power, they still do not think they should have something as boring as a workable plan.

I could go through every false promise made by the Leave campaign from the £350m a week for the NHS to the pledge that German car manufacturers would ensure we could have our cake and eat it. I could present you with the whole life of Boris Johnson from the moment he emerged bawling from the womb. But one scene from January will suffice, because it encapsulated the modern right. Hilary Benn quoted a promise David Davis made in 2016 that Britain would negotiate trade deals far larger than our single market agreement with the EU within two years. Davis could not believe anyone could have believed his bullshit, and burst out laughing. “I think that was before I was a minister,” he said. “That was then and this is now. Ha, ha, ha!”

Jacob Rees-Mogg, right, on Have I Got News For You, has fought a culture war against liberalism. Photograph: Richard Kendal/BBC

Meanwhile, the absolutism with which they fought the culture war against liberalism makes compromise impossible. Compromise would turn them into the kind of politician they have spent their lives attacking: the Europhiles, the experts, the third-wayers, the modernising Tories, the bores. And if habit is not enough to constrain them, they, like their counterparts on the left, are well aware that the smallest deviation from ideological purity will result in cries of betrayal from their former friends.

To take the most shocking instance, many of us warned that Brexit was, in George Orwell’s words, a “playing with fire by people who don’t even know that fire is hot”. In 2016 Daniel Hannan had the integrity to admit his one fear about Brexit was that it would “mess up” relations with Ireland. But rather than compromise, rather than say we must stay in the customs union for the sake of peace in Ireland and frictionless trade through Heathrow and Dover, he now forgets what integrity he possessed and joins the rest of the bullshit right in saying it’s safe to sacrifice the “failed” Good Friday agreement for the greater good of protecting rightwing purity.

The Brexiters are trapped, and their power to force a vote of no confidence in Theresa May means they have taken the prime minister captive too. Last week Tony Blair and Sir John Major expressed their astonishment at how she was failing to level with the public about the economic consequences of leaving the single market. As Major elegantly put it – and there’s a phrase I never thought I’d write – “It is as necessary to speak truth to the people as it is to speak truth to power.”

May has not been speaking truth, and nor has Corbyn. If the PM were ready to take on the right, she would say that the single market forces us to make a hard choice between sovereignty and prosperity. We can have one or the other but not both. On Friday she tried to retreat from absolutist positions: there would be a role for the European court after Brexit, Britain would sign “binding commitments” to maintain regulatory alignment with the EU. The Tory right seemed to accept it, but then they seemed to accept her commitment in her Florence speech to stay in the customs union and single market during the transition phase, only to turn on her later.

They will turn on her again because they have no choice but to find hypocrites and sellouts. That’s what the contrarian pose they have struck teaches them to do. That’s what they must do if they are not themselves to face accusations of selling out.

The new culture on the right was well suited for opposition. In government its irresponsibility, its intransigence and its dilettantish, know-nothing contempt for detail can only lead Britain to ruin.

• Nick Cohen is an Observer columnist