“What’s the difference between a Jew and a Boy Scout?” a friend asked, with a broad grin on his face, as I sat down in my seventh-grade science class. “The Boy Scout comes back from camp!” He and everyone else at my table burst out laughing. Did my classmates even know what they were laughing about? Upset but unsure, I feigned a smile. I am ashamed to say I said nothing. I grew up hearing about the Holocaust through the stories my grandfather, now 92, told about his perilous escape from fascist Italy as a teenager. He described the indifference...