Immigration, the monetary union, and the opacity of so called democracy in Brussels are the achillies heels of the whole failed EU project.  It would have worked if all the nations combined into a superstate (something that will never happen), but to have monetary union without fiscal union makes for a breeding ground for failed states like Greece.

Then there is immigration and freedom of movement.  It's all well for Germany to say to Syrian refugees "come one come all" if they were to stay in Germany, but with the freedom of movement clause in the EU Merkel's decision pretty well is imposed on all member states.  The same goes for any other EU nation.

When you look at France's problems over the past few decades, most of them have had to do with immigration.  The repeated riots some time ago were mostly unemployed Muslim and African immigrants fed up with their miserable lives in cultural ghettoes.  France has been hit the hardest by homegrown Muslim extremism attacks.