In Das Kapital, Marx said that the value of a product was based on the sum of labor that went into it, which is not only very simple minded, but which is obviously very wrong. If anyone doubts this, then just ask yourself whether the price you are willing to pay for an object is determined by the sum of the labor that went into it. The key word there is “willing”. It is your choice, and it is subjective. Economists thus never took Marx seriously. His work was obsolete 3 or 4 years after publication, and he spent the rest of his life trying to quibble and rationalize it. Tom Woods and his guest Phil Magness discuss it here.
Some confusion arises from how Marx conflated capitalism and cronyism, but now the term capitalism is synonymous with economic freedom. In either case, economic freedom—and freedom in general—is clearly superior to Marxist governments, who killed about 100 million of their own people in the 20th century, and who imprisoned or impoverished just about all the rest.
If we stopped here, we might conclude that Marx was possibly a genius, but that he was definitely a fool—but there is more.
Marx had become the leader of the left in Europe, and his tactical advice tailored to each faction played to that faction’s weaknesses instead of its strengths, and his advice thus neutralized the left.
One of the many ways Marx neutralized the left and protected those at the top was that, instead of encouraging the left to attack those at the top, Marx encouraged the left to attack anyone who had more than they did.
We thus see that although Marx may seem like a fool, he was actually a brilliant agent of the most powerful people in the world.