"There seems little point in going through the argument--if only because ... the holders of certain opinions, at a certain level of conviction, are both argument-proof and fact-proof, as was the case with their grandparents in the USSR. It is, unfortunately, only too easy to show that many of the then intelligentsia in the United States, the United Kingdom, and elsewhere were deceived into accepting and supporting a huge fabric of lies. The Soviet Union, despite its horrors, remained acceptable or even praiseworthy, until Kruschev's 'secret speech' of February 1956, and even after that with some.
"But how was it possible? The truth ... was available in scores or hundreds of firsthand accounts. It was clear, too, that foreign correspondents were not admitted to vast areas from which hostile evidence was available. It might even have been thought consequential that dozens of the highest leadership under Stalin simply ceased to be mentioned. The census figures, even as given in 1939, after the public denunciation of a 1937 census as the work of enemy agents, must have been seen as inexplicably low (though in fact even the 1939 census was exaggerated by some three million). Where had the still-missing millions cited seven or eight years earlier got to? And so on, and so on. There were even Westerners who believed that Trotsky was an agent of Hitler. In the second section of this book, we examine the Communist order and all the falsifications that took in the Webbs--not only the Webbs, but a whole mob of others, and this in spite not only of a mass of contrary evidence but even of apparently direct observation. They would often reject these data as irrelevant, and excuse them as, at the worst, superficial defects of a regime heading in the right direction. The USSR also managed to Potemkinize its future--which no evidence, or sense data, could refute."
Robert Conquest, The Dragons of Expectation: Reality and Delusion in the Course of History 50-51 (W.W. Norton & Co., 2005).