I get the gist of what you're saying, but the reality of it is that nationality matters a great deal. It's part of our identity whether you realize it or not. As many immigrants know too well national identity isn't as arbitrary as it seems. It isn't just the exclusion you will face in your new home, there's a strong internal compass that will always point home for many people. It's part of who we are, and a great deal of people have worked hard and sacrificed much for the sake of their country. This picture becomes clearer with age and experience. I celebrate diversity in its many forms. I like new ideas, learning new and different old ways of thinking and doing, but I also know where I come from, and that's as valuable as appreciating others. Maybe even more so.
Nationality is not part of an identity, but nationalism is. I mean that there is no single characteristic which applies to all americans, so obviously there is no part of the 'american' identity which derives from being an american national. However, there is an assignment of values that occurs in people's minds of their particular subculture to 'american' identity.
Identity is too complex a phenomenon to boil it down to such simplistic notions as nationality or political party. Nationalism cannot express a 'whole' identity, and therefore always forces people to ascribe to philosophies which left to their own devices they would not have supported. And that is how we get wars. Thz nation-state is the modern version of the regional tribe, and tribal culture is what causes wars. In that sense, there is no instrument more damaging to human rights than the nation state.
