… is from page 358 of Vol. 19 (Ideas, Persons, and Events  ) of The Collected Works of James M. Buchanan ; specifically, it’s from Jim’s 1997 essay “Reform without Romance: First Principles in Political Economy”:
The simple system of natural liberty, to use Adam Smith’s own designation, or as we would say, the market organization of economic activity, serves two functions simultaneously. Resources are directed by private owners into the most productive activities, as determined by the demands of final consumers, who get, in turn, the largest bundle of goods, again as measured by individuals’ own evaluations. At the same time, however, over and beyond this economic or efficiency-enhancing function, the market reduces or eliminates the need for collective or political choices to be made concerning composition, organization, extent, and distribution of valued product.