… is from page 113 of Paul Krugman’s brilliant article “What Should Trade Negotiators Negotiate About? ” which first appeared in the March 1997 issue of the Journal of Economic Literature (footnote deleted; link added):
If economists ruled the world, there would be no need for a World Trade Organization. The economist’s case for free trade is essentially a unilateral case: a country serves its own interests by pursuing free trade regardless of what other countries may do. Or, as Frederic Bastiat  put it, it makes no more sense to be protectionist because other countries have tariffs than it would to block up our harbors because other countries have rocky coasts. So, if our theories really held sway, there would be no need for trade treaties: global free trade would emerge spontaneously from the unrestricted pursuit of national interest.