Marx was explicit in his claim that socialism is a scientifically derived system of human organization. So far as I can recall, every socialist/Marxist/Communist movement and leader claims a scientific basis for socialism, or at the very least that it is based on unimpeachable common sense. It is famously regarded by its adherents as an inevitable outcome of history. However, consideration of the purported course of socialist evolution reveals that the ideology is not based on science at all, but on magical thinking.
Remember the supposed sequence of socialist development. The revolution involves destruction and as a matter of doctrine revolutionary terrorism. This is succeeded by state terrorism, state control of the means of production and of the entire economy, dictatorship of the proletariat, and eventually the withering away of the state. There are a couple of questions, though. What is the necessary immediate condition to the withering away of the state? It is a population which organically - instinctively - lives according to socialist principles.
This means that the population accepts that each should contribute according to his ability and receive according to his need. Ignore (as socialist thought does) the question of who judges ability and need in the absence of both state and free market. The need and ability formulation requires that in the following scenario, Smith is content. Smith and Jones work in the glove factory. Each is a widower with three healthy daughters aged 5, 9, and 11. Smith's needs are identical to Jones's. Smith shows up at the factory every morning at 5 and puts in 12 hours, producing 300 perfect pairs of gloves each day. Jones is a willing and obedient but incompetent human being. Although he does his absolute best, he is never able to make it to work until 10:30. He leaves work at 5 each afternoon having produced 90 pairs of gloves, 52 of which pass inspection. Smith has a 2 bedroom apartment a mile from the factory. So does Jones. Smith is paid $500 per week. So is Jones. Smith is allotted 2500 calories per day plus 1750 calories per day for each dependent. So is Jones. Each gets a pint of gin per week. And so on.
If you have ever met a person, you know that Smith will not be content with this situation. So how can the purely voluntary end state of socialism, tranquil and cooperative, be brought about? The answer is as simple as it is fatuous: through the process of history an entirely new sort of man - the socialist man - will emerge. Human nature will be fundamentally altered. This is socialist doctrine.
Woody Guthrie mocked Christianity for its promise of what he called "pie in the sky by and by," but it turns out that socialism is nothing more than atheistic millenarianism. Belief in the endless summer day of realized socialism depends on acceptance of the proposition that mankind will inevitably be perfected by time and mute historical tides.
Adherence to socialism - the science of civilization, remember - requires blind faith in the sure and certain perfection of humanity. Every socialist is a deluded moon calf, a true believer in sprites and fairies. That is the worm in the apple.