The eurozone isn’t just a political project held together by political will. In fact, there was always a clear economic rationale behind the creation of the single currency. The euro was supposed to provide Europe’s smaller countries with access to a larger and deeper capital market, sparing them the perennial exchange-rate crises and risk of sudden funding stops that historically saddled them with higher borrowing costs and made it harder to compete in Europe’s single market.

This economic rationale continues to underpin...