He knows all about what makes value, and understands history and how it unfolded, proving him right again and again. Marxists have never really thought about value before, and history? Marxists have been shown to be wrong over and over again. It's just history, Marxists, sorry if you don't have any framework to understand it.
This one is really causing me to twitch. Usually this kind of thing doesn't get to me, but the deep smugness behind the sheer ignorance, the smarmy certainty in their beliefs that are the exact absolute opposite of reality - it doesn't get more pure than this.