Europe wouldn’t necessarily need many shared values to function as a free trade zone. But as a currency union, survival depends on shared economic and political values.
Northern Europe and Southern Europe do not share economic and political values, or a language.
Take a look at this quote from a similar article in Foreign Policy:
A currency union of 17 nations, each with their own tax rates and public sector employment rates and labor market rules -- and above all, their own wildly varying rates of productivity -- cannot last. Either a mechanism has to be found to make them behave more like one another, or the 20-year-old experiment that is the euro, and perhaps even the half-century-old experiment that is the EU, will come to an end.
