I'm getting kind of tired of the whole "Famous person in history did this! Wait - guess who it was - HITLER! gasp " rhetorical trick. I guess it's used to try and paint something in a negative light due to the association with, well, you know, all of that bad Hitler stuff. "If Hitler did it it must have been bad." But also, that old fact of MLK cheating on his wife: we aren't absolute as humans. Hitler really liked dogs or something, right? While I guess it works for shock value and interest, the fact that he did something doesn't then immediately make whatever that thing is evil or tainted. I bet Hitler brushed his teeth, too.
While your point is taken, it's worth noting that when discussing the dark side of empathy, coercion and emotional manipulation the 3rd Reich stands out by any standard. Hitler paid a lot more regard to propaganda than anybody else on the world theatre - Waffen SS uniforms were designed by Hugo Boss. Leni Reifenstahl was given a nearly unlimited budget. Stuka dive bombers were outfitted with noise-makers on their landing gear so the Allies could hear them coming (and be afraid). The Me 262 - a high-speed jet interceptor - was pressed into service as a light bomber (a role it sucked at) so that the Allies would quake in their boots against superior Nazi technology. If we're taking about the downside of propaganda, you're pretty well obligated to mention Hitler, who often favored propaganda over tactics. Aside from arguably the most shocking perpetration of crimes against humanity in the history of the world, the Holocaust was also a dire logistical drain. Godwin's Law certainly, but Hitler ain't exactly six degrees from this discussion, if you know what I mean.
Even Hitler Had a Girlfriend I hear you. The Hitler thing actually does make sense in this context, though it is sloppily presented in that way you are averse to, here. The problem you are highlighting isn't that people treat famous figures as absolutes, but rather that people often treat others as abstract entities. People do this all the time, even for people they've met.
Tell me about it. (I recently had to deal with someone who not only made snap judgements of people's entire personalities mostly based on their appearance and within the first 30 seconds of meeting them, but considered this a positive trait.)People do this all the time, even for people they've met.