If the great history lesson of the 20th century is that socialism does not work then the watershed event in that tragic enlightenment was the one that took place in Moscow 50 years ago this month - the so-called "secret speech" delivered by Nikita Khrushchev to a closed session of the 20th congress of the Soviet Communist party on February 25 1956, in which he mounted a devastating attack on Joseph Stalin, then not quite three years dead.I write this with complete intellectual confidence but also with some journalistic trepidation. Part of me feels the need almost to apologise for writing today about an event from the now-distant past, which for many readers is likely to seem as unrelated to their own lives as the Council of Trent or the Treaty of Unkiar Skelessi. Moreover, as someone raised in the British communist world, whose first memory of any public event is of the death of Stalin himself and who was surprised at the age of five to find that my infant-school teacher had never heard of Harry Pollitt, I am anxious not to disappear into historical anorakland and lose the many readers fortunate enough not to be similarly steeped in the bliss, brutality and betrayal of the revolutionary movement.Yet the secret speech has shaped all of our lives, whoever we are and whether we realise it or not, most obviously because it led eventually to the collapse of the Soviet system, the end of the cold war, and the triumph of the west of which we are all today living if still sometimes conflicted witnesses; but less obviously because it posed questions about public intellectual and political honesty that remain just as undodgeable today as they were in 1956.Given his own history, Khrushchev's speech was an act of great moral bravery and huge political recklessness. Speaking for nearly four hours, he stunned his listeners with a detailed and sweeping account of Stalin's mass arrests, deportations, torture and executions. Though the delegates were sworn to secrecy (and the speech remained unpublished in the USSR until 1988), the details soon leaked out, both in briefings to Soviet and satellite parties and, possibly at Khrushchev's own instigation, to the western media, including via John Rettie of Reuters, later of the Guardian.The truth caved in on us, is how one person in the audience graphically described the speech. But as Tony Judt points out in his magisterial Postwar, it is important not to overstate what Khrushchev was attempting. His aim, not surprisingly, was a controlled de-Stalinisation that kept the revolutionary myth and the Soviet system intact. All the faults of the Bolshevik experience were laid at Stalin's door alone. But in his characteristically impulsive way, Khrushchev placed the possibility of a reformed Soviet system on the agenda. For the next decade, indeed, it was still possible to believe in that outcome, and there were true believers who persuaded themselves that it could happen, even 30 years later in the Gorbachev years. Harold Wilson's "white heat of the technological revolution" speech in 1963 can only be properly understood in the context of his fear that Khrushchev's boast that the USSR would outproduce the US by 1970 was well-founded. But the larger reality, as his biographer William Taubman says, is that the system never recovered from the secret speech and nor did Khrushchev.The most immediate reason for this, especially outside Russia, was the suppression of the Hungarian democratic revolution in November 1956. From that moment on, communism was irrevocably more about oppression than liberation. After Hungary the excuses would not wash, though many still made them (even my own father, in spite of the fact that he, along with the former teachers' leader Max Morris, was one of only two members of the British CP's executive committee to vote to condemn the Soviet invasion). After Hungary, as Judt puts it, communism became "just a way of life to be endured" until, mercifully, its misery and decline came to an end without large-scale bloodshed in 1989.It is of course true that, long before 1956, there had been generations of progressives, socialists of various kinds and even communists who had broken with the Bolshevik myth or who had never embraced it in the first place. Traditions of democratic and moderate socialism that predated the Russian revolution flowed on uninterrupted by 1956. Yet though not directly implicated by 1956 in the way that communists were, these other traditions on the left were challenged and damaged by what Khrushchev said and what the Red Army tanks then did in Budapest.The secret speech was a turning point because, in Eric Hobsbawm's authoritative phrase, while the October revolution created a world communist movement, the 20th congress destroyed it. Experience, whether in the form of Walter Benjamin's backward-looking angel of history or Barbara Tuchman's lantern from the stern (the image is essentially the same), had weighed the left in the balance and found it wanting. After 1956 socialism became more than ever just a matter of religious faith rather than reason. It would take another 30 or more years before that verdict was irrevocable. But it was the secret speech and Hungary that together, as Judt says, shattered the mirror in which the European left had always seen itself.But it shattered something else too. After 1956 it was no longer intellectually honest or true (if it had ever been) to use the cold-war syllogism that my enemy's enemy is my friend. Those who saw history as a long war between good (the left, socialism, the future, the Soviet Union) and evil (the right, capitalism, the old order, the United States) were no longer entitled to swallow their doubts. It was no longer sweet and noble to kill for the cause. A few, of course, still said it was. Even to this day one occasionally encounters the old lie that the Hungarian rising was a counter-revolution.But the cold-war syllogism lives on today in a new guise. Too many haters of capitalism and the United States still cram everything into the frame of untruth and self-deception that says my enemy's enemy is still my friend because, even if he blows up my family on the tube, murders my colleagues on the bus or threatens to behead me for publishing a drawing, he is still at war with Bush, Blair and Berlusconi. It is 50 years this month since that simplistic view of the world lost whatever moral purchase it may once have had. It is time such thinking was, to choose a sadly appropriate word, purged. Too long, my brothers and my sisters, too long.