Single currencies tend to favour the rich and impoverish the poor. They do so because changing the value of your currency, and varying your interest rate, is the way that disadvantaged places can make their goods more affordable. When you prevent them from doing that, you trap whole cities and regions – the poorest people in the poorest places – without being able to trade their way out.
Across a continent, the effects are so much worse. That’s why Ireland’s economy has been overheating, while east Germany’s is languishing in poverty. That’s the danger of the euro as presently arranged, and don’t underestimate it.
The real question, now that the euro is being re-organised, is this: can a civilised and peaceful Europe survive that kind of Napoleonic control where the rich countries are so favoured by the currency?