The only problem is that you ignore the nature of men and his history. Nation states are a relatively new thing. People used to live in city states, principataes, and that sort of thing, but then you get Persia for example who wants more and more territory and to rule everyone, then you get Rome, Alexander of Macedonia, Islamists in 600s, etc.
I think we all want to be one world with no border without any government whatsoever. It is unfortunate however that a government is needed.
Personally, I favour Aristocracy combined with some form of accountability to the people. Thus a combination of Aristocracy and democracy.