Personally I blame lead poisoning and decades of propaganda, mind you this only really affects Gen X and the Boomers but the younger dipshits can just be explained by the memetic equivalent of the founder effect.
I mostly subscribe to this because I've met plenty of dumb silent generation who are not nearly this fucken asanine, sure they tended to be stubborn and weirdly racist but honestly hating the Russians and Germans is pretty acceptable to this shit.