The reason the U.S. economy can work at all is because people in the union accept large continuous transfers of money from rich to poor states.

For the Euro to work, the rich member countries must be willing to accept massive transfers from countries like France and Germany, to the Mediterranean countries. In addition, the ECB must be a lender of last resort.

Seeing as none of these criteria are currently (formally) met, the Euro can't function. The only way it could work was if the economies of the member states quickly converged. They didn't.