… is from page 6 of Bruce Caldwell’s superb “Introduction” to the 2007 Definitive Edition (Bruce Caldwell, ed.) of F.A. Hayek’s classic 1944 volume, The Road to Serfdom  (footnote excluded; the quotation within is from page 182 of the 1997 reprint, in F.A. Hayek, Socialism and War: Essays, Documents, and Reviews , of Hayek’s 1938 essay “Freedom and the Economic System”):
In the 1938 version [of an essay that Hayek wrote preliminary to The Road to Serfdom], though he continued to stress the links between fascism and socialism, Hayek began to expand on what he saw as the fatal flaw of socialist planning – namely, that it “presupposes a much more complete agreement on the relative importance of the different ends than actually exists, and that, in consequence, in order to be able to plan, the planning authority must impose upon the people that detailed code of values which is lacking.” He followed with a much fuller exposition of why even democratic planning, if it were to be successfully carried out, eventually requires the authorities to use a variety of means, from propaganda to coercion, to implement the plan.