I don't like fireworks all that much, but damn it, I love my country, right or wrong.
And that, folks, is exactly the problem.
I generally agree with a lot of what has been said on this thread. On the face of it, there isn't anything wrong with acknowledging that the United States has been a great place and has, through its existence, made other parts of the world better as well. In fact, it would seem to be a good thing. However, such sentiments tend strongly towards cultivating the notion that the United States is somehow superior, or inherently better, neither of which is true, and also creates complacency towards the very goodness we are supposed to epitomize.
Nationalism, even patriotism, is dangerous for that reason. Many people, I would go so far as to say most people, are completely incapable of understanding that past greatness does not imply present greatness or future greatness. Moreover, they tend to believe that pride in one's institutions also means being uncritical of them, as if they cannot be improved. This is not only an American phenomenon, to be certain; it exists in China as cultivated by the government, in Japan as pride in the emperor, manifest by far-right political parties in Europe, etc. But it is an extremely dangerous one, and one I feel we could do without.
I'm just an American by coincidence, nothing more. I'm glad I was lucky to be born somewhere with a high standard of living and a great deal of social freedom, but there are places in the world that are just as good, if not better. And, even if there weren't, it would still be merely coincidence.