Paul Krugman makes a simple but facially compelling argument that the usual difficulties associated with dissolving or shrinking the European monetary union wouldn’t apply come the worst-case scenario in Greece:
. . . [A]ny move to leave the euro would require time and preparation, and during the transition period there would be devastating bank runs. So the idea of a euro breakup was a non-starter.
. . .[B]ut what if the bank runs and financial crisis happen anyway? In that case the marginal cost of leaving falls dramatically, and in fact the decision may effectively be taken out of policymakers’ hands.
Actually, Argentina’s departure from the convertibility law had some of that aspect. A deliberate decision to change the law would have triggered a banking crisis; but by 2001 a banking crisis was already in full swing, as were emergency restrictions on bank withdrawals. So the infeasible became feasible.
Think of it this way: the Greek government cannot announce a policy of leaving the euro — and I’m sure it has no intention of doing that. But at this point it’s all too easy to imagine a default on debt, triggering a crisis of confidence, which forces the government to impose a banking holiday — and at that point the logic of hanging on to the common currency come hell or high water becomes a lot less compelling.
And if Greece is in effect forced out of the euro, what happens to other shaky members?