It's not so much not understanding,that would be ignorance, indifference or being oblivious.
It that the 1930's German populace thought they understood all too well, they had very definite ideas.
It was racially, religious, and socio-economic, driven. Centuries of historical developments in the making.
Demonization of the out-group is a psychological mechanism that dates back to the stone age. It's tribal. And it's likely encoded in the genes. It's that much a part of out evolutionary development. Close knit tribal allegiance, the psychological dynamics of that were essential for survival, for hundreds of thousand years, if not going back millions, going back to our primordial ancestors.
I say all this, because I'm a History buff. I know alot about WW2.

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AQ: 27 Diagnosis:High functioning (just on the cusp of normal.) IQ:131 (somewhat inflated result but ego-flattering) DNA:XY Location: UK. Eyes: Blue. Hair: Brown. Height:6'1 Celebrity I most resemble: Tom hardy. Favorite Band: The Doors. Personality: uhhm ....(what can i say...we asd people are strange)