Walter Lippmann, Public opinion (New York: Harcourt, Brace and Company, 1922), 108 (chap. 8, "Blind spots and their value"). But progressivism (an obsession with material progress) is here one of those "stereotypes" that creates "blind spots", and blind spots cover "up some fact, which if . . . taken into account, would check the vital movement that the stereotype provokes." Their value is that they "keep away distracting images, which, with their attendant emotions, might cause hesitation and infirmity of purpose. Consequently the stereotype not only saves time in a busy life and is a defense of our position in society, but [unfortunately] tends [also] to preserve us from all the bewildering effect of trying to see the world whole steadily and see it whole" (114).
I was put onto this by Thomas C. Leonard, Illilberal reformers: race, eugenics & American economics in the Progressive Era (Princeton and Oxford: Princeton University Press, 2016), 194n23.