You mean cause everyone thinks they're the good guys right? Cause the US is definitely not the good guys.
And yet, there are bad guys. Churchill was a bastard, and no kind of “good guy” yet Hitler and the Nazis were the bad guys. C‘est la vie. Stalin was one of the bad guys, and so was Slobodan Milosovic, and so is Dick Cheney, Tony Blair, Pol Pot, etc. Good guy is a tough category to fill, but history is full of inexcusable monsters and we should be careful with our moral relativism.
But I agree with your main point. There is real evil out there and we have a moral prerogative to stop/fight/kill those people.
The USA is hardly spotless, but they have a good reputation of standing up to real evil in the world.