I know what you’re thinking: this is going to be a very long post. To cover all the ways in which Karl Marx went wrong would take volumes (and volumes have been written on this very subject). But this post is going to cover every what in which Marx went wrong. Instead it’s going to focus on one specific failure: the idea of a vanguard party.
Marxism, and philosophies based on Marxism, advocate for a revolution by the proletariat (working class) to overthrow the bourgeois (holders of capital). After the revolution concludes Marxism argues that a vanguard party, made up entirely of people from the proletariat, must claim dictatorial control and use that control to guide humanity towards the socialist future.
Socialism, by itself, isn’t a terrible idea. Ensuring everybody in a society has the bear necessities of survival is a bit utopian but not an evil idea in of itself. Having a society where everybody enjoys the same rights is a damned good idea. Both of these are two of the primary goals of socialism. Under Marxism these goals are to take the form of laws enforced at gunpoint by a vanguard party.
Marxism falls apart because it attempts to create social equality using social inequality. The vanguard party, by its very nature, has privileges other members in a society lack. It has a monopoly on interpreting the “true” definition of socialism. Every program it puts into place is based on its interpretation. The vanguard party quickly becomes the new ruling class and the proletariat merely becomes the new bourgeois.
History has demonstrated all of this. Think of every Marxist revolution. Russia, China, Cambodia, Vietnam, and North Korea were or are nations where the old ruling party was replaced by a vanguard party based, at least in some amount, on Marxism. Social equality never gained a foothold in any of those nations. They were instead turned into authoritarian states where anybody not liked by the new ruling party were declared bourgeois and eliminated. The dictatorships of the proletariat became no different, and sometimes far worse, than the former rulers in frighteningly short order.
I think the key failure of Marxism is its reliance on coercive hierarchy. One cannot bring equality about by establishing inequality. As soon as one group has coercive hierarchy over another equality is destroyed. Compounding that is the tendency for power to attract vicious individuals. The Soviet Union would almost certainly have been far different is Stain hadn’t succeeded Lenin. But when Lenin died the most ruthless replacement, Stalin, was able to seize power and bring a reign of terror to the fledgeling union. Death wasn’t enough to remove Stalin’s authoritarianism from the Soviet Union. His actions justified more vicious actions by his predecessor. The result of the October Revolution wasn’t social equal, it was a society starkly divide between members of the Communist Party and everybody else.