Isn't it obvious by now what this is about? Our need to prove that Hitler was not "normal," thus not like us, normal human nature thereby exculpated from producing a Hitler. It fills a need to reassure ourselves there is no Hitler potential in human potential. We're off the hook.
I can appreciate Rosenbaum's exasperation with revisionist folk history, but asking people to accept Hitler as human--as someone like themselves--is like pleading for the sun to stop rising in the morning.
Human beings have a powerful tendency to disavow and externalize deeply disturbing wishes and fantasies. Nazis are ideal containers for these fantasies.
And although Rosenbaum is right about a defensive function for these 'urban legends,' the persistent sexual dimension of these legends isn't merely a defensive cover to dehumanize and distance ourselves from a murderous Hitler. The perverse sexual dimensions of these urban legends are themselves more directly tied to unsettling elements of our own sexuality.
The spit and polish discipline, the themes of torture, power, helplessness, degradation and humiliation associated with Nazi imagery touch on primitive sadomasochistic dimensions of human sexuality. The insistent fantasy of a one-testicle Hitler, in particular, hints at disavowed castration anxieties. A genitally defective Hitler provides males with a material indication that we are sexually 'normal.'
To be clear, I'm not disagreeing with Rosenbaum's thesis about the fundamentally defensive function of these urban legends. I merely suggesting that these legends do more than defend against awareness of the aggresive monsters within. They are defensive solutions to anxiety about the sexual monsters within, as well.