Remember in Blues Brothers when they end up at the Nazi rally and the point isn't even that Jake really hates Nazis, it's that Nazis are about the biggest losers that anyone could imagine. They are portrayed as completely pathetic dead-ender assholes.

Or in the Rocketeer when the mobsters find our the Sinclair guy is a Nazi and join forces with the FBI to stop them because Nazis are clearly the worst thing.

Or when Christopher Plummer rips the Nazi flag in two in Sound of Music.

None of these films were making bold political statements. The Nazis were the bad guys because that was something that everyone in the audience could agree one. Dunking on Nazis was a guaranteed crowd pleaser.

When the hell did we stop agreeing on something so simple and self-evident as Nazis Are Fucking Losers?

@theropologist Another factor that comes to my mind is the push to feel "different" from the mainstream culture to find validation in being nonconformist. What's than more attractive then rooting for the universally despised bad guys? That combined with right wing groups strongly defined identity that can give a sense of belonging to those who conform. I guess this mix can be quite attracting for marginalized people