The harm done…was that they removed economics from reality. The task of economics, as many [successors] of the classical economists practiced it, was to deal not with events as they really happened, but only with forces that contributed in some not clearly defined manner to the emergence of what really happened.
Economics did not actually aim at explaining the formation of market prices, but at the description of something that together with other factors played a certain, not clearly described role in this process. Virtually it did not deal with real living beings, but with a phantom, "economic man", a creature essentially different from real man.
Ludwig von Mises, The Ultimate Foundation of Economic Science