To the list of questions the left has sought to place off limits to open debate—global warming, same-sex marriage, campaign finance, abortion—add a startling new topic: monetary reform. And what a scalp has just been claimed.

Alan Greenspan, who was chairman of the Federal Reserve for nearly two decades, has pulled out of a conference this summer on monetary reform. He did so May 8, two days after the New York Times published a blog post by Paul Krugman labeling Mr. Greenspan the Fed’s “worst ex-chairman ever.”

Mr. Krugman was set off by word that Mr. Greenspan had been billed as one of the speakers for a counter-conference that is set to take place in Jackson Hole, Wyoming, in late August, as the Federal Reserve holds its annual retreat there. Mr. Greenspan declined to comment on why he has withdrawn, but the conference’s sponsor, the American Principles Project, confirmed to me that he did so in the wake of Mr. Krugman’s attack.

The conferees plan to continue nonetheless, and just as Congress itself is fermenting on the need to reform the way monetary policy is made. And so the mightiest central bank in the world will be in one conference center, while its critics will gather in another venue down the street. The proceedings of the reformers will be open to the public: a classic teaching moment.

Yet it horrifies Mr. Krugman, who reacted by attacking . . .

The full text of this column can be read here at the Wall Street Journal.