Dani Rodrik in Boston Review:
A journalist calls an economics professor for his view on whether free trade is a good idea. The professor responds enthusiastically in the affirmative. The journalist then goes undercover as a student in the professor's advanced graduate seminar on international trade. He poses the same question: Is free trade good? This time the professor is stymied. “What do you mean by ‘good?’” he responds. “And good for whom?” The professor then launches into an extensive exegesis that will ultimately culminate in a heavily hedged statement: “So if the long list of conditions I have just described are satisfied, and assuming we can tax the beneficiaries to compensate the losers, freer trade has the potential to increase everyone's well being.” If he is in an expansive mood, the professor might add that the effect of free trade on an economy's long-term growth rate is not clear either and would depend on an altogether different set of requirements.
This professor is rather different from the one the journalist encountered previously. On the record, he exudes self-confidence, not reticence, about the appropriate policy. There is one and only one model, at least as far as the public conversation is concerned, and there is a single correct answer regardless of context. Strangely, the professor deems the knowledge that he imparts to his advanced students to be inappropriate (or dangerous) for the general public. Why?
The roots of such behavior lie deep in the sociology and the culture of the economics profession. But one important motive is the zeal to display the profession's crown jewels in untarnished form—market efficiency, the invisible hand, comparative advantage—and to shield them from attack by self-interested barbarians, namely the protectionists. Unfortunately, these economists typically ignore the barbarians on the other side of the issue—financiers and multinational corporations whose motives are no purer and who are all too ready to hijack these ideas for their own benefit.
More here.