The EU has shown that if you have a monetary union, without a political union, problems are bound to crop up.
Countries like Greece which could have benefited from fiscal stimulus and depreciation of currency don't have the room to implement it. So countries will be wary.
It is not problem of political vs economic union. The problem lies in different level of development of EU countries.
EU is not monolith. There are rich countries like Germany, France, UK and very poor like Greece, Poland, Estonia.