Actually Marx's number one flaw was identical to laissez faire capitalists...
He believed you could have an automatic economy that could take the place of government and essentially run on its own with no problems.
In addition he failed to predict a lot of things like the creation of unions and labor regulations, which helped make things easier for workers so they didn't revolt.
But what the hell? We're not all Nostradomus.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside