I had written something very long and nonsensical about all this, but what I have to say boils down to this — life is full of attachments and affections that aren’t strictly rationally defensible and there’s nothing wrong with that. Indeed, life would be terribly dull without such attachments. But what distinguishes the liberal’s approach to his patriotism from, well, the wrong approach is that a liberal will recognize the contingency of it. Most people love the country where they were born and raised and think it’s the finest in the world. Intelligent people don’t lose that love, but they do recognize that, in fact, they love their country because they were born and raised there and not because it is, in fact, the finest in the world. That doesn’t mean you stop loving your country, but it does mean that you open yourself up to other kinds of affections both bigger and smaller than “the nation” and also recognize that there’s a circumscribed relevance to this sort of thing.
But a cosmopolitan in the real world doesn’t become one by purging himself of particularist affections, rather he multiplies them and recognizes that others have affections of their own and that these sentiments are all owed a certain amount of respect and consideration.
Lurking behind really dogmatic professions of universalism, especially in the political arena, tends to be an especially rancid form of nationalistic hubris — think of George W. Bush proclaiming that American interests and American ideals are one and the same and also completely congruent with the demands of the universal human yearning for freedom.