Answer:
Because it happened, we must understand the evil, the systematic evil, the state-sponsored evil, industrialized killing, mass murders that were the essence of the Holocaust. We must understand its emblematic invention, the death camp, and the people who served in these camps. Their assignment: mass murder. Some were sadists and criminals—people unlike us—but many more were ordinary men trying to do their best, to fulfill their obligations. Some were even professionals, lawyers and doctors, ministers and economists who used the skills they had learned to become more efficient killers. Some were enthusiastic, others more reluctant; all became killers.