Dan was posing a hypothetical about somebody writing a book focused on the positive things that came about as a result of Nazi Germany, the Holocaust and World War 2. His point was that it would be extremely difficult for such a book to be received positively because of the emotion that such themes and events evoke in people affected by Hitler’s and Nazi Germany’s actions.
He was using the Nazi Germany analogy to parallel his own experience in college when he produced a paper focused on Mongol military tactics during the reign of Genghis Khan. Dan explained that his lecturer or supervisor made the comment that while the paper was good, it failed to address the atrocities (specifically the sexual violence) carried out by the Mongols. Dan says that he couldn’t understand why that was relevant to a paper focused on military tactics but later on understood that for someone like his lecturer (who I think he says was of Chinese heritage) it was difficult to seperate anything positive that might have come from the Mongolian conquests with the scale of the atrocities they committed.
His point here is that despite the vast amount of time that has passed since those atrocities were committed, there remains a deep cultural pain among those cultures that suffered. The Nazi Germany analogy is used to help explain how cultural memory is not restricted to those who directly experienced the events but could endure for centuries.