Considering that the people posting this "creative irreverence" were the same guys calling you a "stupid f*gg*t n*gger piece of sh*t" on Halo 2/3 and CS when they got noscoped from across the map or whatever, "It's just a joke" has always been somewhat suspect. It would be wrong to say that there was no element of tongue-in-cheek-iness and hyperbole, of course. It just wasn't completely innocent, broadly speaking.

Of course, in a post-Bioshock Infinite world, there's really no excuse for not grokking how time and distance from the origins of a cultural behavior pattern can warp even well-meaning notions that aren't regularly re-examined and tuned to align the intention with the zeitgeist. If the Sarah Silverman-esque posters ever looked up and realized, "Oh, they don't know it's a joke, they're ACTUALLY Nazis," it was too late to shift things back. (Unless you were in a Boondocks thread on /co/, in which case correction was freely forthcoming.)

Probably didn't help that at least one mod wanted 4chan to become more racist, on purpose.