Ethno-nationalism strikes me as the default mode of social organization. Throughout all of human history-- even unto today-- men have organized themselves according to ethno-sameness. The only difference today is that the oligarchy disapproves and has an aggressive agenda of multi-culturalism, so we are all under the vague impression that there is something vicious about a so-called "ethno-state." Yet the northeast liberals still ogranize themselves in small, posh communities behind gates. Hollywood has its walls and borders and guess what? No brothers or day laborers to be seen. So even if on the macro level the social engineers have managed to blur the ethno-significance of their states, once you zoom in to other levels its obvious how people organize themselves.
Of course this doesn't necessarily prove that such organization is right, only that it is the tendency of man to so organize. To show that it's right, or at least that there's nothing wrong with it, does not the Church's reticence on the issue through hundreds if not thousands of years speak volumes? The multicultural state is incredibly new, the traditional state encountered by the Church was one of ethno-natives, and I am completely unaware of her ever rebuking the composition or organization of these states.