It was socialists who saw the dangers of Communism first and most clearly. In 1918, at the dawn of the Soviet era, Karl Kautsky, who had personally known Marx and Engels in his youth, wrote a diatribe against Lenin's use of the vague Marxist term "dictatorship of the proletariat."
Kautsky insisted it had been meant metaphorically, and that genuine class struggle presupposed genuine democracy. The so-called dictatorship of the proletariat "always leads to the dictatorship of a single man, or of a small knot of leaders" and to a situation where ordinary people "only become instruments for carrying out orders."
From Andrew O'Hehir's review of 'The Rise and Fall of Communism' by Archie Brown, in Salon.com.
One thing was not a historical fluke or accident, though: the fact that a political system based on some half-baked utopian musing by Marx and Engels, and their bogus claims of scientific certainty, was not going to work out well for anybody.
There's room for argument about whether it had to turn out quite as badly as it did, and plenty of room for discussing the continuing validity of Marx's insights into capitalism. But there's no denying that the works of a philosopher who championed human creativity became the basis for a social system devoted to crushing it. It's the platonic ideal of historical irony, to which other historical ironies can only aspire, and suggests some very dark possibilities about human nature.