The Nazis were complete shits on an unprecedented scale, but there was quite a bit of "demented evil" done by Americans too in WWII, like carpet-bombing European cities and interning citizens of Japanese ancestry.
The world has never been simple. "Black & white" is always a result of hegemonic propaganda more than actual conditions. It so just happens that certain strains of propaganda seem particularly ineffective on the most creative personalities of our age; but it takes very little for things to change. A lot of stuff produced in all media between 2011-09-11 and 2013-03-14 was very black & white, and without that senseless invasion we'd probably have many more monodimensional "Arab baddies" around today.
The film was set during WW2. If you portray Captain America punching Iraqi soldiers in 2004, well yeah your film deserves to fail.
But is it as mythically important that a sandal-wearing goatsherd from Helmand province (AK-47-totting or not) gets punched in the face by Just a Kid from Brooklyn?
What about Captain America punching civilians in Sarajevo, as the Sarajevo TV building is being bombed in the background?
Iraqi soldiers confronting the invasion of their country by the US army, being punched in the face by Cap?
Cap punching little Vietnamese women and children in My Lai?
What I mean is that the world itself has changed quite a bit since the time of the Nazis. In terms of dramatic evil, no modern "bad guys" can do unambiguous, demented evil as well as the Nazis used to. And the good guys don't look that unambiguously, selflessly good themselves anymore, either. In fact, if you ask me (and I'm a westerner) they look more and more like the bad guys themselves.
Maybe comics can't just go on pretending the world is all black and white, when most of us can see around us that this is not the case.