A post-national Europe?

I have signed the manifesto of the Spinelli group for a united Europe. I am absolutely in favour of a federal, integrated, more democratic European Union. I think that nationalism stands in the way of this objective, and that achieving it is more necessary than ever to collectively solve our social and economic problems. There are no national solutions to most of todays' problems: climate change, global poverty, financial instability... However, manifestos only allow for the decision to sign them or not, but blogs make it possible to qualify the decision. And my qualification in this case has two parts:
-In an ideal world, a Europe devoid of nationalism would be great, but I think that plans for a future Europe should be more realistic about the nature of humans in society. Nationalism is an evolved feature of human societies, one that appeared in hunter-gatherer societies to jointly fight enemies external to the group and that will not disappear just because Daniel Cohn-Bendit and his friends wish so. It would be better to think of a future united Europe that provides a framework to deal with the many problems of societies with conflicting, diverse and overlapping national identities.
-I think some of the people who have signed the manifesto are at the same time promoting initiatives in their own countries that undermine the objectives of the Spinelli group. To be honest, for example, I wonder how the Catalan nationalist conservative MEP Mr. Ramon Tremosa can at the same time be signing in favour of removing the frontiers inside Europe, and actively promoting the independence of Catalonia, thus pushing for a more fragmented Europe, with more frontiers rather than less. I would have prefered to sign a manifesto where the promoters are more careful about the bed-fellows they attract.