For me, the terrible reality of real-world wars and military conflicts is trivialised when referenced or used as a setting within the fantasy world of superhero comics. So Captain America punching Hitler or Superman destroying enemy tanks in WWII is not a cool thing in my eyes.

But thing I think is dangerous about Nazi villains in superhero stories in particular is that because it's so easy to present them as obviously and straightforwardly evil, it reinforces the tendency of readers to enjoy vicariously the moral superiority of the superheroes they identify with, just as they revel in the fantasies of physical power these characters were created to embody.