Interestingly, Marx loathed philosophy and insisted his theories were science, not philosophy:
“We recognize only one single science, the science of history. You can view it from two sides, and divide it into the history of nature and the history of people... . In direct opposition to German philosophy which came down from heaven to earth, we here intend to rise from earth to heaven — that is we will not start from what people say, imagine, represent to themselves, nor from thought-of, represented or imagined people, in order to arrive afterward at bodily people; we will start from really acting people, and try to deduce from their actual life-process the development of these ideological images and reflections of that life-process. For these misty formations in the brains of people are necessary sublimations of their material, empirically ascertained life-process, which is bound up with material conditions. In this way morals, religion, metaphysics, and other forms of ideology, lose their apparent independence. They have no history, they have no development; only people, developing their material production and their material relations, change also in the course of this activity their thinking and the products of their thinking... .
“Thus where speculation stops, that is, at the threshold of real life, a real positive science begins, a representation of the activity, the practical process of the development of people. Phrases about consciousness disappear, their place to be occupied by real knowledge. When you begin to describe reality, then an independent philosophy loses its reason for being. In its place may be found, at the most, a summary of the general results abstracted from an investigation of the historical development of man... .
Any kook or quack can claim that their ideas are "scientific", but that does not make them so.
Very often, kooks use a language similar to that of science and claim a scientific basis for whatever they are advocating, but their purpose is to lend credibility to their ideas so as to impress people who are naive about the methodologies of real science and do not understand its language.
In making a judgment about the scientific validity of such a claim (i.e. that socialism is based in science), one must look at whether there is supporting evidence. True, I have no desire to study Marx, but I have never heard any claim that he undertook any kind of hypothesis-driven scientific study (whether observational or experimental), the carefully analyzed results of which led him to the conclusion that socialism is, in fact, a natural and workable model for human society.
A statement out of your quote, "For these misty formations in the brains of people are necessary sublimations of their material, empirically ascertained life-process, which is bound up with material conditions," is as good an example of pseudoscience as I have ever seen. He put sciency words together, but they express no coherent science-based principle or observation.