The eurozone's monetary problem
We have a basic structural problem with the eurozone. Yes, it's entirely true that having the same currency across different economies increases the possibilities of trade. Not all that much if we're honest about it though. It was the creation of the Single Market rather than the single currency which drove economic integration.
The problem is that the currency area is too large - we've too much variation in economic conditions. For one currency, by definition, means one monetary policy. If we've different conditions in different parts of that wide zone