Great article on where bad policy ideas come from and why they stick:

There is no inexorable evolutionary march that replaces our bad, old ideas with smart, new ones. If anything, the story of the last few decades of international relations can just as easily be read as the maddening persistence of dubious thinking. Like crab grass and kudzu, misguided notions are frustratingly resilient, hard to stamp out no matter how much trouble they have caused in the past and no matter how many scholarly studies have undermined their basic claims.

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Perhaps the most obvious reason why foolish ideas persist is that someone has an interest in defending or promoting them. Although open debate is supposed to weed out dubious ideas and allow facts and logic to guide the policy process, it often doesn’t work that way. Self-interested actors who are deeply committed to a particular agenda can distort the marketplace of ideas.

Stephan M. Walt, “Where Do Bad Ideas Come From (And Why Don’t They Go Away)?,” Foreign Policy, Jan/Feb 2011