What did Mr. Ross’s reaction to the questions posed by his history class tell you about his character?

The students are stunned, and many ask why no one tried to stop the Holocaust. Mr. Ross suggests several reasons—for example that, the Nazis were highly organized—but explains that ultimately, no one knows. I think Mr. Ross does understand mob mentality but doesn't know how to explain it to his students. Mr. Ross is a very passionate teacher: he wants his class to have an understanding of why the German population went along with Hitler.