The reason it's so upsetting is precisely for the reasons you state. I (perhaps foolishly?) believe that America has the opportunity to be a role model for the rest of the world in terms of how a society can work.
America has its problems. I will be the first to agree with that.
But for all its problems, America has a lot going for it. It's a relatively free society, there is social mobility (more for some than others, it's true) and it's a nice place to live, even just in terms of its geography. (I live in California and so that of course will make me biased).
Consider - America is a country that, despite all its problems, people risk their lives to get into. There's a simple reason why America continues to attract illegal immigrants - it's better than wherever they came from. So much so that they'll pay sleazy people to transport them across borders under the cover of night. It sounds dramatic, but that's because it is!
So - America is great and I'd personally like it to stay that way. That's why it's the responsibility of the people living in America to keep their backyard clean and their politicians in line.