I'm neither an america expert or an history/political expert, but as far as I can tell, is the american society full of "flaws" and things that should have been otherwise.
I'm not saying that one political system is better than another, but I would rather live in a socialist-ish political society, than an american.
About the nationalism:
Nationalism is important, and you cannot say that "since the nazism hid behind nationalism, nationalism is bad", or "extreme nationalism ended in war, nationalism is bad".
As etkenn mentioned nationalism led to two world wars, but he forgot that extreme nationalism was only one of several things that led to war..
Nationalism is also what makes different countries different (culture wise).
Nationalism today is what saves our cultural treasures, and it has been an important part of the society since the national romantic time (end of 19. century).