Marxism can probably be classified as either political theory or slick propaganda. The key question is this: Was Karl Marx' goal to promote socialism (which was born before Marx) or derail it? Or was his goal to simply manipulate it for some sinister purpose?
According to Wikipedia,
It has been claimed—though controversially—that there were elements of
socialist thought in the politics of classical Greek philosophers
Plato and Aristotle.
In this spirit, aren't traditional "native" cultures largely communistic? Imagine traveling back in time a few hundred years and offering a Sioux hunter a choice between 1) bartering for something of value, or 2) two buffalo robes for the price of one...provided he close the deal by 6 p.m. Eastern Standard Time on Friday.
Some authorities believe Christianity was embraced and molded by the Romans, who valued it for its propaganda value. (The phrase "Render unto Caesar what is Caesar's" certainly made a great political slogan.) Similarly, some people believe postmodernism is the creation of propagandists - or a philosophical school they have molded, similar to the Romans.
The first modern "Self-conscious" socialist movements were reportedly born in the 1820's. Karl Marx was born in 1818.
The early history of the Soviet Union (the first socialist state) was amazingly bloody. Socialism/communism was successful in that the USSR evolved into a superpower, exceeded in power only by the U.S. But life in Eastern Europe was hardly a workers' paradise.
Of course, Karl Marx was hopefully sincere in his quest to create a worker's paradise. He may have been horrified by the Soviet experiment if he had lived long enough to witness it.
I don't understand Marxism well enough to comment on it in detail. I'm a huge fan of socialism, in the broad sense of the term. There's a huge difference between the Soviet Union and Cuba, Libya or Canada's health care system.
One thing that popped into my mind just recently is Marxism's emphasis on workers. While I would rally behind a movement that supported workers over corporate interests, what about farmers?
To me, Marxism sounds like an urban school, strangely out of place in the vast Soviet empire, which relied heavily on agriculture. Under Lenin, land was taken away by farmers - a great way to subjugate a population. (Read about the Holdomor.)
I may be rambling. Like I said, Karl Marx might not have approved of the Soviet experiment, which may not have even been true to Marxism.
However, I wouldn't compare Marxism to science fiction unless it was - gasp - nothing more than a slick propaganda campaign. It could be compared to prophecy in the sense that its growing popularity was almost inevitable.
People desperate to escape the horrors of capitalism - the exploited class - would obviously look for an alternative, and socialism appears to be the only major alternative economic system. Unfortunately, such people could easily get suckered by smooth-talking propagandists.