Opposing fascist movements ought to be the easiest of the tasks. Who but the depraved can excuse Russia as it engages in a war of imperial aggrandisement, murders and rapes civilians, and so loses itself in irredentist fantasy that it hopes to get away with denying the very existence of Ukraine?

For many, however, anti-fascism is a holding position. The followers of the worst parts of the left (I will get to the right later) will oppose barbarism if, and only if, the barbarians are Westerners or Western allies. Imagine if the EU, UK, and US were indifferent to Putin’s aggression or supported him. It is not such a hard thought experiment to perform. Russian money has flooded the western financial system, and the Obama administration and European Union did next-to-nothing when Russia invaded and annexed Crimea in 2014.

If Western governments were pro-Putin, the far left would know what to do. Trade unions would unfurl their banners, the Socialist Workers Party would manufacture “Defend Ukraine” placards, and demonstrators would stop the traffic in Parliament Square.

But because the West is belatedly opposing Putin and arming the Ukrainian resistance, the kind of anti-imperial leftist who venerates Noam Chomsky, and cheered on the takeover of the Labour party by Jeremy Corbyn and his supporters, stays at home. Western support changes everything for them, even though nothing has changed in Ukraine. The mass graves and rapes, the destruction of cities and abduction of civilians, would still have happened regardless of whether the West ignored or condemned Russia.

The worst type of leftist may not actively support Russia, in public at least, but excuses or ignores its crimes because their monomaniacal detestation of their own society prevents them sharing solidarity — that most admirable of left-wing values -— with the victims of a vicious imperialist adventure.

Or as Corbyn’s Stop the War movement explained: “Our focus is on the policies of the British government, which have poured oil on the fire throughout this episode. In taking this position, we do not endorse the nature or conduct of either the Russian or Ukrainian regimes.” Moral equivalence is it, then? Russia launches an unprovoked invasion of Ukraine and there’s nothing to choose between the combatants?

Before analysing this political equivalent of an oppressive compulsive disorder, let me dispense with the other explanation for the collapse in principle.

From the point of view of Russian nationalists, Putin’s insane war is worse than a crime; it’s a blunder that may tear the empire to pieces. One day — soon, I hope — the Kremlin archives will be thrown open and we will find out who Russian money bought in the UK. Many journalists suspect that the suborned will not only include London libel lawyers and City bankers but political actors and “opinion formers” too. Indeed, I can make a fair stab at guessing a few of the names today.

But I am equally sure that most Putin apologists have not been corrupted. Russia did not need to waste money bribing them because they were eager to provide propaganda free of charge. Here is how they move from civilisation to barbarism. If you are on the Fox News or Ukip right and believe progressive values have irredeemably corrupted your country and the wider West, you cannot see your country’s true enemies. Indeed, you support them as the populist right from America to Hungary supported Putin because he was anti-gay, anti-liberal and anti EU. To put it another way; if you believe that today’s great struggle is against woke progressives waging a war against Western culture, you are likely to have nothing to say when Vladimir Putin begins an actual war.

What applies to the populist right applies to the far left. Condemning your society is what stirs your blood and motivates your life. You become hyper-alert to its high crimes and minor hypocrisies. I can describe the delusion that follows because I experienced it myself when Tony Blair was prime minister. I despised the spin and mediocrity of his government so deeply I could not shift my attention and see the 9/11 attacks for the atrocities they were.

I was hardly alone. Many involved in political debate fall into monomania and end up as dangerous absurdities. It ought to be simple enough to fight the corruption and incompetence of the Johnson administration, for instance, while saying it has saved a shred of its honour by providing effective help to Ukraine. Any well-rounded person ought to have the humility to accept that, however severe and scandalous the UK’s problems may be, the suffering of Ukrainians supersedes them. But the ability to walk and chew gum at the same time is a gift not everyone possesses. Like the Corbynistas in Stop the War, they can only focus on “the policies of the British government”.

In our time, obsessives have dominated politics. They all but killed the Labour Party and turned the Tories into a rabble incapable of providing prosperity or security.

They ought to have taught us, if we did not already know, that the road to hell is a single-lane highway filled not with good intentions but with one-track minds.