… is from page 226 of James Buchanan ‘s 1979 collection What Should Economists Do?  (H. Geoffrey Brennan & Robert D. Tollison, eds); specifically, it’s from Buchanan’s May 1978 American Economic Review essay “Markets, States, and the Extent of Morals”:
What can a person be predicted to do when the external institutions force upon him a role in a community that extends beyond his moral-ethical limits? The tension shifts toward the self-interest pole of behavior; moral-ethical principles are necessarily sublimated. The shift is exaggerated when a person realizes that others in the extended community of arbitrary and basically amoral size will find themselves in positions comparable to his own.