America is unique, it is better than many other countries on many fields, worse than some on other fields, and America has made great historical achievements. I say that as a non-American: America has indeed done a great job spreading, preserving and defending freedom and democracy on this planet. Without America, I couldn't live in freedom today here in Germany, and I am very grateful. America is probably the one foreign country I feel closest to. Also, America is the most important ally of my country these days.
So Americans have reasons to be proud.
But that doesn't mean I don't find some kinds of American nationalism silly. Pride in your own country and its achievements is one thing, but looking down on others is another. Also, some nationalistic American myths are just that, they are either exaggerated or emphasize an alleged exceptionalism that doesn't exist any longer. When patriotism comes with chauvinism and ignorance, it's pretty ugly, not only when Americans do it, but also when Americans do it. And sometimes, it seems that those who are most vocal about their patriotism are those who have the least knowledge about other countries and places on this planet.
For example, sometimes you meet Americans who have never been to Europe, don't speak a language other than English, yet believe America is better than Europe, because Europe allegedly is a "socialist" hellhole, because Europeans allegedly don't know what freedom is, etc pp. People who make jokes about Nazis and "cheese eating surrender monkeys" not just in jest, but take these stereotypes way too seriously. Ignoring that freedom and democracy have a long tradition in countries like France, the Netherlands or Switzerland too, and ignoring that fact that most of Europe today is not any less free than America (some European countries are even more free, if you believe certain indexes).
What's also silly is when an individual American believes the world, or people of other nationalities, owe him anything, although he himself probably has never done anything constructive to improve America, or even the rest of the world, but just waves the American flag. Just because the American nation did many great things in history, it doesn't mean every backwards redneck was part of it. I feel great gratitude towards the achievements of American soldiers who liberated my country, and I have great repect for Americans who help fostering their and my values within and outside of their country, but that doesn't mean I need to kiss the butts of ignorant random Americans who were born long after that, just because they happened to be born into that club.
I hope nobody gets me the wrong way when I write that. I don't think the ignorant or rah rah patriots are a majority in America, on the contrary. And I know for sure that such horrible people exist in every country, definitely in my country as well. They exist in America too, and they can be annoying. They draw the wrong conclusions from the myth of American exceptionalism and get it the wrong way.
So I'd say Americans have all reason to be proud on their country, America is indeed exceptional on some fields, not so much on others, and on some fields, others are better. But Americans don't have any more reason to look down on others, or condemn them, than non-Americans. An "exeptionalism" that is understood as a blank cheque to mock or loathe other nationalities is misguided.