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.

Across the continent, political divisions are deepening. For all of these reasons, the specter of a euro zone collapse has not been dispatched.

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.

For those unfortunate enough to experience it, long-term unemployment - now, as in the 1930s - is a tragedy. And, for society as a whole, there is the danger that the productive capacity of a significant portion of the labour force will be impaired.

While holding the eurozone together will be costly and difficult and painful for the politicians, breaking it up will be even more costly and more difficult.

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.

The 24% unemployment reached at the depths of the Great Depression was no picnic.