"..." Europe is one of the great, inspiring stories of the modern world, maybe of all time: peace, prosperity, and democracy flourishing where once there were minefields and barbed wire.
But: the strategy depends on each move toward economic integration being both a political symbol and a good economic idea. That was clearly true of coal and steel, the common market, the eurosausage, and so on. It is, however, by no means clear that the euro passes that test. Europe’s limited labor mobility (although there’s more than there used to be) and, crucially, lack of fiscal integration makes a common currency a dubious proposition at best. "...."
Paul Krugman, Prémio Nobel da Economia