When is a dictator not a dictator? When he's on the Left, apparently. Over the past 48 hours, Fidel Castro has attracted revolting euolgies, not only from unapologetic Marxists, but from a number of politicians who think of themselves as democratic socialists.

Here, to pluck an example more or less at random, is the Blairite minister, Peter Hain: "Castro's troops inflicted first defeat on South Africa's troops in Angola in 1988, a vital turning point in the struggle against apartheid."

Yes, Peter, Castro opposed apartheid, or at least backed Marxist Angola. He also opposed the Prague Spring, dismissing the Czech democracy activists as "fascists". It's worth noting, en passant, that Castro's Cuba had the same racial hierarchies as other Caribbean states, with most black people living in squalor. Castro encouraged black Cubans to enlist in his African war partly to displace Cuba's racial problems. As a good Leninist, he knew all about countries "exporting their internal contradictions".

Not that I want to pick on Peter Hain. Here is Gianni Pittella, leader of the Socialist Group in Brussels, an alliance of moderate Social Democrat Parties: "‪Fidel ensured peace, social and cultural equality to Cuba. We hope the path of openness will be continued."

Seriously? Social and cultural equality? In a regime where opponents were interned and tortured? A regime that exiled nearly two million people? A regime that actively supported FARC and the IRA. Peace?

"Why is it that dictators of the Left are not scorned in the same way as those of the Right?" asked the Nobel Prize-winning Peruvian novelist Mario Vargas Llosa. "Was General [Augusto] Pinochet, in his 17 years in power, crueller or bloodier than Fidel Castro has been in his decades ruling Cuba?"

Good question. Both men crushed opposition parties, closed down hostile media, suspended parliamentary democracy, repressed dissidents and filled the administration with their friends and families. The main difference is that, unlike Castro, Pinochet eventually submitted himself to the ballot box, offering Chileans a referendum in 1988 on whether they wanted to keep him. By 57% to 43%, they voted "No", and Pinochet grumpily stomped off the stage.

Castro, by contrast, didn't even bother with the Potemkin democracy of Eastern Europe: those "elections" in which Communists would supposedly form an agreed list along with members of the Agrarians, the Social Democrats and other satellite parties. As he put it in 1963: "The revolution has no time for elections!"

So why the double-standard from people who, in other circumstances, think of themselves as democrats? When I called Castro a dictator on a BBC radio debate yesterday, the other guest, a spokesman for the Cuba Solidarity Campaign, protested that he had toppled a "a genuine dictator [Fulgencio Batista] who was in the pocket of the Americans". Ah, yes, the Americans. You can rule, as Castro did, through the internment camp and the firing squad. You can reduce your country to misery. It's all OK, provided you're sufficiently anti-American.

In fairness, my fellow guest – an angry fellow – may not set great store by democracy. There has always been a Trotskyist strain in Britain, which sees the people as being liable to what Engels called "false consciousness" – that is, a tendency for workers to be led astray by bourgeois propaganda to the point where they will no longer vote in their own interest. But that hardly applies to the Hains and the Pittellas.

Tweeting your support for Castro, like wearing a T-shirt with the image of his comrade, Che Guevara, is a way of signalling that you feel strongly enough about your principles to do violence in their name.

What we're seeing, rather, is the enduring appeal of radical chic, a phenomenon personified by that prize ass Jean-Paul Sartre, who became obsessed with the Cuban revolutionaries. Tweeting your support for Castro, like wearing a T-shirt with the image of his comrade, Che Guevara, is a way of signalling that you feel strongly enough about your principles to do violence in their name. You may never fire a shot yourself, but hey, these revolutionaries did; maybe some of their sex appeal will rub off on you through your T-shirt.

The attraction is especially strong, these days, for men in their sixties who began as Communist students, but ended up as milquetoast Social Democrats or New Labour ministers. Latin America was the great cause of radical students in the 1970s, like South Africa in the 1980s or Palestine today. In reliving their youthful passions, they are also recalling the simplicity of their younger world-view, the us-and-them division between heroes and reactionaries.

Part of that world-view is that the ends justify the means and that, in words of Alexander Kerensky's that came into vogue during the 1930s, there are "no enemies to the Left". So titanic was the People's Struggle that details like torture might be overlooked. In fairness, there were also Cold Warriors who applied a mirror justification to Right-Wing dictators, including Batista and Pinochet. "He may be a son-of-a-bitch, but he's our son-of-a-bitch".

Fidel Castro
Cuban leader Fidel Castro dies at 90 Reuters/Prensa Latina/File Photo

It's an old phenomenon, this selective blindness to the faults of people on "our" side. Psychologists call it self-serving bias, and Orwell noticed it at the very beginning of what was to become the Cold War. Here he is writing in 1945:

"The Daily Worker disapproves of dictatorship in Athens, the Catholic Herald disapproves of dictatorship in Belgrade. There is no one who is able to say — at least, no one who has the chance to say in a newspaper of big circulation — that this whole dirty game of spheres of influence, quislings, purges, deportation, one-party elections and 100% plebiscites is morally the same whether it is done by ourselves, the Russians or the Nazis."

Of course, these self-serving biases should have become redundant after 1990. Both sides were now free to update their morality. Never mind: "He may be a son-of-a-bitch, but he's our son-of-a-bitch". Try: "He may be our son-of-a-bitch, but he's a son-of-a-bitch."

If they were coming fresh to Castro today, most Leftists would indeed be appalled by his human rights abuses, his anti-gay campaigns, his crushing of dissident writers and intellectuals. But, human nature being what it is, once we have picked our team, we tend unconsciously to filter out negative stories about it.

And so the last generation of Trotskyite students, now for the most part paunchy and greying Blairites, defend the glamorous fatigue-clad guerrilla and mourn the certainties of their younger days. The rest of us breathe a sigh of relief that Cuba might finally taste freedom.

"History will absolve me!" a young Fidel is supposed to have told the judge when on trial after a failed uprising in 1953. Al contrario, Comandante. History has already damned you.

Daniel Hannan has been Conservative MEP for the South East of England since 1999, and is Secretary-General of the Alliance of European Conservatives and Reformists