I’m so grateful to Jim DeLong for finding this ungated version  of the Henry Hazlitt  -edited collection The Critics of Keynesian Economics . (Jim tells me in an e-mail that an essay in this book that he especially likes is the one by David McCord Wright . I concur.)
In Hazlitt’s collection is reprinted this choice and profound passage from page 409 of Hayek’s 1941 book The Pure Theory of Capital :
I cannot help regarding the increasing concentration on short-run effects–which in this context amounts to the same thing as concentration on purely monetary factors–not only as a serious and dangerous intellectual error, but as a betrayal of the main duty of the economist and a grave menace to our civilization. To the understanding of the forces which determine the day-to-day changes of business, the economist has probably little to contribute that the man of affairs does not know better. It used, however, to be regarded as the duty and the privilege of the economist to study and to stress the long effects which are apt to be hidden to the untrained eye, and to leave the concern about the more immediate effects to the practical man, who in any event would see only the latter and nothing else. The aim and effect of two hundred years of continuous development of economic thought have essentially been to lead us away from, and “behind,” the more superficial monetary mechanism and to bring out the real forces which guide long-run development. I do not wish to deny that the preoccupation with the “real” as distinguished from the monetary aspects of the problems may sometimes have gone too far. But this can be no excuse for the present tendencies which have already gone far towards taking us back to the pre-scientific stage of economics, when the whole working of the price mechanism was not yet understood, and only the problems of the impact of a varying money stream on a supply of goods and services with given prices aroused interest. It is not surprising that Mr. Keynes finds his views anticipated by the mercantilist writers and gifted amateurs: concern with the surface phenomena has always marked the first stage of the scientific approach to our subject. But it is alarming to see that after we have once gone through the process of developing a systematic account of those forces which in the long run determine prices and production, we are now called upon to scrap it, in order to replace it by the short-sighted philosophy of the business man raised to the dignity of a science. Are we not even told that, “since in the long run we are all dead,” policy should be guided entirely by short-run considerations? I fear that these believers in the principle of apres nous le deluge may get what they have bargained for sooner than they wish.