I started reading a book on economics a couple of years back. There was a whole section on Karl Marx, how he had studied economics in detail, and had a deeper knowledge of economics than almost anyone in history. I stopped reading at that point.
Karl Marx had a Ph.D. from a German university and if he had not been a political radical might have had a successful career as a professor at a German university (he was a baptized Jew so I don’t think his Jewish ancestry would have barred him from a career). He was smart—just extremely wrongheaded. Claudius Ptolemaeus was a brilliant scientist—but his Ptolemaic theory of the solar system is completely wrong. Marx is the Ptolemy of modern economic thought.