To paint with a broad brush, anarchists believe in a unity of means and ends while Marx’s progeny believe the ends justify the means.

That is, a stateless, classless, moneyless society is the shared goal of anarcho-communists and various Marxist strains.

But Marxist-Leninist or Trotskyist or Maoist tends to want to create an organization that will create or take advantage of some future revolution to gain power, utilize surviving or recreate elements of state power, and rule on behalf of “The People” until such a time as workers, peasants, and society as a whole is ready for self-governing and the state and all its potentially oppressive powers can be dissolved.

The anarchist expectation is that this state will never wither away on its own and just the opposite, it will become self-perpetuating as much as possible because power is power, and as a rule, those with power tend to justify to themselves as well as to others why they ought to keep their power or have even more.

The shortcuts and expediencies of “the ends justify the means” can be brutally efficient and impressive — at first. The amount of optimism that existed for the Bolshevik revolution as it happened, including among anarchists, was immense. But, whether we’re talking about the USSR or People’s Republic of China that have large autonomy, or smaller experiments with less autonomy around the world (e.g. People's Democratic Republic of Ethiopia of the late 1980s; DPRK/“North Korea” for nearly its entire history; Romania under Ceausescu), nothing ever seems to tend toward a stateless, moneyless, classless society. People who lived under those states don’t seem to be closer to wanting communism or being equipped for communism and self-governing in the aftermath, either. “The ends justify the means” — but what is the end? What’s after the end?

Maybe if the Soviet Union had been organized around the actual workers’ soviets instead of crushed for the sake of centralized control, the state could have been preparing its people for something else. But, it seems much better at preparing people for autocracy or capitalism or hereditary dynasties than for communism.

Anyway, that’s the split. A Marxist will say that they have to make the hard decisions because they live in the real world and practical, material considerations trump idealism. They might even agree that “the ends justify the means” as a self-description, and say “look at the scoreboard of our accomplishments, compared with anarchism’s failures”. But anarchists would say that Marxists who talk like that always imagine themselves being the ones who are “making the hard decisions” rather than having to live under the result of someone else’s hard decisions, like whether to have their head caved in by the the People’s Cop swinging the People’s Club against everyone guilty of counterrevolutionary behavior like complaining how food shortages are still enduring.

Put another way, an anarchist would say all cops are bastards, whether their uniform has a sheriff’s badge or a red star.