Barry Eichengreen — American Economist

Barry Eichengreen is an American economist who holds the title of George C. Pardee and Helen N. Pardee Professor of Economics and Political Science at the University of California, Berkeley, where he has taught since 1987. Eichengreen's mother is Lucille Eichengreen, a Holocaust survivor and author... (wikipedia)

The 24% unemployment reached at the depths of the Great Depression was no picnic.
The consequences of a collapse would not be pretty. Whichever country precipitated it - Germany by threatening to abandon the euro, or Greece or Spain by actually doing so - would trigger economic chaos and incur its neighbours' wrath.
As for the single market, the E.U.'s landmark achievement, there is no question that a euro zone breakup would severely disrupt its operation in the short run.
Political union means transferring the prerogatives of national legislatures to the European parliament, which would then decide how to structure Europe's fiscal, banking, and monetary union.
The 1992 crisis proved that the existing system was unstable. Not moving forward to the euro would have set up Europe for even more disruptive crises.