The denial of the Holocaust has no more credibility than the assertion that the earth is flat. Yet there are those who insist that the death of six million Jews in Nazi concentration camps is nothing but a hoax perpetrated by a powerful Zionist conspiracy. Forty years ago, such notions were the province of pseudohistorians who argued that Hitler never meant to kill the Jews, and that only a few hundred thousand died in the camps from disease; they also argued that the Allied bombings of...