It's hokey, but its true -- USA offers opportunity like few other nations in history, and its culture wants to do the right thing.
1) There's never been an aristocracy, and even most of the wealthy consider themselves middle class. With education (not always as available as should be), work, and good fortune anyone can succeed. Some make it big time, but far more important are the average folks who move up steadily. My paternal great grandfather was an Irish wheelwright, my grandfather was executive in charge of food service for Eastern Airlines, my father a computer systems analyst. Another graeat grandfather was a coal miner, and my maternal grandfather was a depression era subsistance farmer. My mom was a nurse, and I'm a professional. No upper class to look down on me, no one to spite me because my ancestors were from a certain group. Nobody gets respect because of who they were born to -- we value who they are. As a country, we seem to think that most problems have a solution, and while we sometimes grab an easy answer we at least try to do something. We're not perfect by any means, and I'm often embarassed by my countrymen -- but I'm glad I was born where I was.
2) "realpolitik" -- as I understand it, tempering the "right" thing with compromise to get a "good" thing done -- has never caught on here. IN the Imperialist era, when US "aquired" possessions as "protectorates", we expressly planned to give freedom and self government to those possessions. Although I'm a little ashamed at how we defined "rebels" in the 1900-1920 period, we had explicit timelines and programs in place before WW2 to give freedom to the phillipines by the 40s; unlike the european powers whose concerns after the war lead to political and military fights to keep their possessions. Freedom and justice motivate us to altruistic acts -- like intervention in wars that have less than obvious impact on our country. We went to Somalia to stabilize and feed a country, because it seemed like the right thing to do. In fact, values play such a role in our culture that even when politicians are crass and manipulating they have to pay lip service to justice. That's why politician's "moral failings" (hwever you chose to define them) play such a substantial role here that europeans often dont see what the big deal is. Yes, we make mistakes, and like an impetuous teenager we may react before thinking everything thru. We are often more sure of ourselves than we should be, and we may not listen to afvice that well.
But, we're there when needed. Even when people are brutal or ungrateful, we're there. As for "third world countries" that we "can't handle" -- that's only because we want to do what's right. If we wanted to be fascist, no htird world country on earth could last a month. Iraq looks troubled because we limit ourselves -- if we chose to behave like Saddam or Idi Amin or Assad even King Hussein, Iraq would have been "pacified" long ago. Saddam used chemical weapons for YEARS, incontrovertibly, adn the UN ignored him. (It got so bad that the inspectors, when asked to evaluate the possiblity of chem weapons use in the 80's refused to produce another report -- they said the facts are known, and the next question is what to do about the facts.) The free world did nothing, ignoring human rights abuses that resulted in the deaths of thousands. The world ignores slavery in Sudan. The world ignores a lot of evil.
So why is so much attention and anger directed to the US? We try to do something where we can. We are reviled for going to Iraq. We DID SOMETHING about a man who did much evil. Should we have "contained" him? SHould we have "contained" Hitler in europe, leaving the french, belgians, austrians, poles, czechs, et al. to be liquidated gradually? Those living under the Nazis would not have appreciated that, and in any case it was RIGHT to fight for the freedom of others. We certainly could have isolated Hitler in europe, adn it would have saved American lives without materially harming us. OK, continental europe would have all fallen under the Iron Curtain, but europeans like us to be isolationist anyway.
Economics are not everything, but opportunity IS valuable. Freedom is great, and the US has arguably done more to export it than any country in history. WE're not always right, we may be on average historicaly and culturally ignorant -- but its still a great place. The world has been a better place because the USA existed.