On the topic of Brad deLong's contentious column, the perils of prophecy, there is this nice post on the Naked Keynesianism blog: Sensible theory and economic predictions (July 13, 2011)

Economists are well known for having predicted nine of the last five recessions.  Or so goes the joke.  The fact that economists cannot predict and that forecasters are always wrong is not new, and I would suggest less important than often understood.  The problem is not so much that economists cannot predict particular events, but that the dominant theory is an ineffective tool for understanding real economies. And that is true for both the New Classical/Real business Cycle types that believe that markets are efficient immediately, or the imperfectionist New Keynesian, that think that they are too, but only in the long run (this view should lead you to believe that the main solution is to reduce imperfections). As a result, the mainstream always provides unreasonable predictions.

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Not only deregulation was something good for Europe, but also giving up the currency would allow for lower interest rates and higher growth.  For him [Rudiger Dornbusch, in 1990]:

"Having a national money is expensive ... It offers little flexibility and year after year an interest cost is paid for what is the illusion of independence. ... Monetary sovereignty nowadays means only the right to bad money.  How can the periphery get out of the self-inflicted historical curse of a central bank and a national money. Do what Argentina did ... Give up the national money and create a hard link to a world class currency."

It goes without saying that this does not sound like good advice these days.  And before you say that hindsight is always 20-20, I want to remind you that yes some people that were in favor of the European project actually saw the limitations of the euro.  The economists that did not believe in the efficiency of markets (at least not for allocating resources, including labor) argued that giving up a tool (like the exchange rate) would imply the need for other tools.  Here is Wynne Godley in 1992, about the project of a common currency for Europe:

"It needs to be emphasised at the start that the establishment of a single currency in the EC would indeed bring to an end the sovereignty of its component nations and their power to take independent action on major issues. ... the power to issue its own money, to make drafts on its own central bank, is the main thing which defines national independence. If a country gives up or loses this power, it acquires the status of a local authority or colony. Local authorities and regions obviously cannot devalue. But they also lose the power to finance deficits through money creation while other methods of raising finance are subject to central regulation. Nor can they change interest rates. As local authorities possess none of the instruments of macro-economic policy, their political choice is confined to relatively minor matters of emphasis - a bit more education here, a bit less infrastructure there."

If you are not convinced, try it on someone who has not been entirely debauched by economics. — Piero Sraffa