(1) people think cooperation is a good idea

(2) and they also want to keep their own countries and identities

Once we start moving towards a single country, the inevitable question becomes, which rules and values should people follow? Which country gets to assert its way of life on the others? Or perhaps the virtual state known as the "EU" should assert its own values (whatever they may be)?

Now imagine expanding the EU to Turkey. Can we change their legislation to be more liberal? Or should the EU countries follow the hard line authoritarian islam that Erdogan pushes? No one is willing to change. And no one has to as long as the EU stays as a form of cooperation between nations.

If the EU pushes towards a single country, power struggles over values will follow.