I take the point that the dark/light trope had its origins in political battles in Britain against the Treasury View.  The question still remains, why was that trope thought relevant and appropriate to the rather different conditions of the US, and who thought it so?  And why, if so inappropriate, has the trope proven so lasting?

For those who don't subscribe to the NYRB, I quote the hook that opens Krugman's piece:  "The history of economic thought in the twentieth century is a bit like the history of Christianity in the sixteenth century.  Until John Maynard Keynes published The General Theory of Employment, Interest, and Money in 1936, economics--at least in the English-speaking world--was completely dominated by free-market orthodoxy.  Heresies would occasionally pop up, but they were always suppressed.  Classical economics, wrote Keynes in 1936, 'conquered England as completely as the Holy Inquisition conquered Spain.'"

Note the startling (Christian) religion analogy (which is continued in the next paragraph:  "If Keynes was Luther, Friedman was Ignatius of Loyola, founder of the Jesuits.")  Note also how England stands in for the entire "English-speaking world".  These are interesting rhetorical moves as well, albeit familiar.  
Also for those who don't subscribe, I wish I could reproduce the picture that illustrates the first page:   Arnold Schwarzenegger (famously foreign born and hence unPresidential) with his arm around Milton Friedman in 2004.  Interesting choice, presumably the editor's not Krugman's, but not an idle choice given the vast number of photos available.  What is that all about?  

Perry Mehrling

[The entire article is freely available online at
http://www.nybooks.com/articles/19857
HB]