… is from page 167 of Vol. 19 (Ideas, Persons, and Events  ) of The Collected Works of James M. Buchanan; specifically, it’s from Jim’s 1986 paper “Liberty, Market and the State”:
The abiding genius of Karl Marx lies precisely here, in his acute understanding of the possible reaction of the ignorant intellectual to the workings of the capitalist or market order.
DBx: Fancying themselves to be unusually insightful, thoughtful, and knowledgeable, a great many intellectuals are, in fact, mindless pack animals. They mistake their slogans – which sound fine to the ears of intelligent second-graders – for insight and knowledge. Never bothering to learn economics, and also never bothering to think realistically about politics or to study history with care, they criticize without careful reflection, condemn without sound judgment, and propose without information, insight, or wisdom.