The Euro was the first step to a Federalised Europe, each country eventually losing their national identity to a centralised government.
Yes trade in Europe is essential, but a central government is nuts. Centralised power becomes unwieldy and expensively unproductive. Also the major economies will not end up supporting the ones with less GDP. This is already evident.
In the last few years we have noticed how the French youth have changed, they are not so polite. The French youngsters used to be delightful. Always deferential, even to us Brits. Now the teenagers barely respond to a 'Bonjour'. This is in the Breton countryside so I wonder how less polite they are in towns.
To us, this is the biggest erosion of 'Frenchness'. The loss of identity for the French youth.