"nationalism: it emerged in response to particular felt needs, as the human community/consciousness is expanded and/or refined through cosmopolitan experiences those felt needs change, and hence, people who act on that basis of nationalism are invoking something that human beings have moved beyond, or at least should be moving beyond."

I'm sorry but there can be no argument against this...
except to say that such cosmopolitanism can not be enforced from without, whether in Kosovo or the US. If it could be I would be in favor of doing so in my country (the US). As it is there's more sophisticated discussion of politics in the teahouses of Tehran than there is here.
Whether Europe's old blood is willing to recognize it or not, the new cosmopolitanism is here, and it includes Islam. The Islamists in Turkey are more modern than the military secularists, and are more modern than the arch-secularists in the west: Dawkins et al. According to Steven Weinberg Zionism is science. (see Chapter 15) If thats the case, so is the Trinity.
The rule of reason is the rule of experts, who spout language most people don't understand. And it's also the rule of experts who in their arrogance will twist reason into their own perverse definition of the reasonable. Weinberg did just that. And that's the danger of the rule of men. Communities who prefer the rule of community as such have every reason to rebel against this. But in time, and not under threat, all communities will learn.
Some things can't be taught. Modernity, as the secularism of law and democracy (and not the secularism of Platonism and pseudo-science) must be learned, and earned. The question of Kosovo is whether stability and "progress" is best served by specific actions in specific places at this time. If one wants to play the neutral observer then one's own ego and desire to be publicly on the side of the angels or of righteousness is irrelevant.

"The compromises that people make, the sacrifices they forgo, may trouble a philosopher who is obsessed with human rights. But "I don't believe," says Walzer, "that the opposition of philosophers is a sufficient ground for military invasion."

This is simply truly obvious. To say otherwise is the logic of those without any second order awareness of themselves and of the world.

Russell Arben Fox is a believer and I'm a secularist. But his faith incorporates doubt and his opponents' faith does not. The choice is easy.