Once many, decades ago I watched a TV interview with Albert Speer (the "architect" of the 3rd Reich). There were a couple of things that really stuck in my mind.
In one he and Dan Rather (I think it was) watched a short video of Hitler playing the children and his dog (a German Shepard of course ). Rather commented that it seemed so strange to see this "monster" looking so normal. This was the one time where Speer became very agitated. He said, no, no you must not think of him as some sort of monster. Someone separate and different from all of us. If we do that we forget to be on the alert for others like him. Not his exact words of course but I got his point as being that we must recognize the dark side of humans and not treat the beasts like Hitler as "not true humans". As individuals we may have more or less of this darkness but we must not forget or ignore the possibility in anyone.