What some people are pleased to call “hope” ended for me in a Moscow taxi in the early 1990s. I was in the front and reached for my seatbelt, but the driver stopped me because seatbelts were just another bit of unmourned communist authoritarianism. Hurtling through Moscow in that rickety car I suddenly understood the incredible desire for freedom that had recently smashed the Berlin Wall.

I was witnessing the death of a monstrous lie in which I had somehow, through a mixture of idealism, anger, alienation and intellectual pride, managed to implicate myself. Not long before the Berlin Wall was overwhelmed, I was invited to join the Communist Party of Great Britain (CPGB) in the Cambridge branch of Sainsburys. I said yes. It was the culmination of my student years as a serious and committed Marxist.

Karl Marx was a gentle man, but his ideas would lead to human suffering almost unequalled in the history of the world

Now here I was in Russia, eating soup swimming with sausage fat in the decaying hostel of the Komsomol – the international communist youth league founded in Moscow in 1918 – realising that I had subscribed to a world view whose actual existing, concrete and cardboard reality was one of the most inhuman and murderous follies ever dreamed up in the fevered minds of zealous thinkers.

Karl Marx was a gentle man, but his ideas would lead to human suffering almost unequalled in the history of the world. On the best current figures, about 6 million Russians were murdered in the era of Joseph Stalin – and that’s before you factor in the sufferings of eastern Europe from 1945 onwards, or the other revolutions from China to Cuba.

Today, the terrifying reality of Marxism in power has been consigned mercifully to the history books, but it has strange echoes. Clearly, Jeremy Corbyn is no Stalin, or Lenin, or Mao Zedong, just a long-serving British MP, but Marxist ideas live again in some spectral form in Corbyn’s runaway campaign and the enthusiasm of his supporters for a truly socialist Labour party. In one of the unspun answers that makes him appear authentic to supporters, Corbyn called Marx “a fascinating figure who observed a great deal and from whom we can learn a great deal”.

Of course, the Daily Mail leaps on words like that as in 1924 it leapt on the fake Zinoviev letter in an attempt to smear the Labour party. I am not calling Corbyn a Marxist – and anyway so what, I used to be one myself. In truth, the mood of the new model left is more romantic than scientific, and Marxists were always scientific. But I think that on the left you – we – have to face up to what was done in the name of an extreme version of socialism in the 20th century.

That’s been forgotten by too many people since the 2008 financial crisis started what looks to many like a true and profound “crisis of capitalism”. A runaway banking system and a society that seems to hugely favour the rich have since inflamed the radical socialist conscience that now seems poised to make the Labour party its voice. The Capital de nos jours may be Thomas Piketty’s book rather than old Karl’s but in its fervour, enthusiasm and optimism it refuses to see that it drags behind it the chains of a brutal history.

Marxist ideas live again in some spectral form in Jeremy Corbyn’s runaway campaign 

This is about morality. It is about what it is right and proper to believe in the light of all we have learned about what the far left did to human souls when it actually got a chance to engineer them. I can’t listen any more to rhetoric that contrasts the idealism of Corbyn’s supporters with the supposed cynicism, hollowed-out power worship and futile pragmatism of the centre-left. I am a Labour centrist supporter not out of cynicism but out of principle, because I believe the only ethical politics of the left today has to be moderate, reasoning, and sceptical. I am Labour, but I am not a socialist any more.

What really shocked me when I saw the last days of the Soviet world was not its totalitarianism. Everyone knew about that. But as a socialist student in the 1980s I’d absorbed the notion that the USSR was a “state capitalist” system that never achieved true socialism. That illusion crumbled when I queued for gruel ladled out from huge tubs at Moscow airport and bought a drink at a shop where there were separate tills for each of the small range of commodities. I was seeing pure socialism – and everyone I met was exploding with joy to escape from it.

I don’t think that after the fall of communism you can reject the capitalist economy root and branch or want to subject it to strong state control as Corbyn does. Markets are human, they have a powerfully creative side as well as a harsh unjust side, and to believe otherwise is to indulge in the same folly that killed the hapless peasants who Stalin labelled capitalist “kulaks” and saw fit to starve and shoot. The anti-market obsession that has overtaken the thinking left since Lehman Brothers is a treason by intellectuals whose hypocrisy is glaring. It’s like the old Monty Python gag. What has capitalism ever done for us – apart from the clothes, the food, the computers, the films, the pop music, and all the other stuff people swarmed the Berlin Wall 26 years ago to get their share of?

So what then of hope? This is what we are told Corbynism has unleashed. If markets rule OK and capitalism goes on for ever, where’s the hope that things can change? The most serious answer is that, yes, there really has been a great loss of that kind of radical “hope” since 1989 exposed the evil madness of the Great Socialist Utopia. Islamic fundamentalism, for instance, gets a lot of its appeal by filling the space left by the lost dreams of Marxism that once inspired revolutionaries all over the world.

Marxist socialism really was a powerful, attractive source of hope for the workers of the world, once. But it led to mass murder and a slowly crumbling edifice of banal deceit that has permanently shattered the idea of utopia. When Thomas More dreamed of a communist utopia in 16th-century Britain, he gave the world a word and a dream that grew alongside the capitalist market itself. Today’s reborn British left echoes the romantic strain of William Morris’s utopian Marxism and ultimately even More - why can’t everything be different?

My favourite Marxist history book was The World Turned Upside Down by Christopher Hill, which rediscovers the lost dreams of radical groups in the English civil war. At university, entranced by Marxist historians like Hill, Eric Hobsbawm and EP Thompson, I tried to prove the civil war really was a class revolution. To sustain that argument I identified prosperous villagers in the 17th century English countryside as “bourgeois peasants”, taking the idea from the “kulak” class theorised by Marxists in early 20th Russia. But there never was a kulak class. Those “theorists” invented it to justify a savage assault on peasant society that killed millions, not only by shooting but enforced famine.The trouble with Marxist thinking is that in pursuit of a utopian logic it reduces human beings to abstractions. It is easy to murder an abstraction.

I never did fill out my CPGB application in the end. Anyway, as people who remember the 80s will know, Marxism Today magazine was home to a sombre analysis of the left’s prospects launched by Hobsbawm’s 1978 essay The Forward March of Labour Halted. But still, as people in eastern Europe pushed more and more boldly at what would soon be revealed as walls printed with worthless Leninist phrases that turned to dust at the touch, there I was, imagining kulaks. I can’t help thinking today’s bold neo-Marxist concepts like “the 1%” and “austerity” are equally unmoored from real lives. Indeed Greece has already found out what anti-austerity means in practice.

In Russia I came across Marxism Today in a news kiosk in Volgograd – that is, Stalingrad. And beside the vast silver emptiness of the Volga, the kulaks were nowhere to be found.

• This article was amended on 1 September 2015. An earlier version said incorrectly that Marxism Today was funded by Moscow.