Yeah, that thinking went out for western nations in WWI. Even the first Gulf War was supposed to be about human rights (even though it was later revealed we were hoodwinked.) The US 'tries' to be the good guy, they are rarely perceived this way or portrayed this way by media and the public.
I liken the US to Joxer the Mighty from Xena Warrior Hottie. He is 'technically' a hero, he tries very hard to do what is right and noble and usually ends up with egg on his face or derided for the effort. And then occassionally, it pans out. My opinion only, I ask no one else to subscribe to my newsletter.