Thus, as the Eurosceptics warned, a single currency leads to loss of sovereignty, which sounds like an abstract idea until you get a crisis like this. It applies even to the more economically successful countries. If the eurozone is to survive, Germany may have to keep rates lower than it might wish, risking inflation. Eventually, like Greece, it will have to accept greater EU control over public spending levels. Neither country can run a wholly independent fiscal policy within the eurozone, any more than Cardiff or London can within the sterling zone.
You could argue that, with proper democratic controls, a single European treasury would be good for everybody. But the pro-Europeans never made that argument, preferring to insist that the loss of sovereignty was an illusion.
The same arguments being used to sell the idea of a global government, I might point out!