Inigo Montoya: You keep using that word. I do not think it means what you think it means.
Third, according to the most recent compendium of history’s worst atrocities, Matthew White's Great Big Book of Horrible Things (Norton, 2011), religions have been responsible for 13 of the 100 worst mass killings in history, resulting in 47 million deaths. Communism has been responsible for 6 mass killings and 67 million deaths. If defenders of religion want to crow, “We were only responsible for 47 million murders—Communism was worse!”, they are welcome to do so, but it is not an impressive argument.
Fourth, many religious massacres took place in centuries in which the world’s population was far smaller. Crusaders, for example, killed 1 million people in world of 400 million, for a genocide rate that exceeds that of the Nazi Holocaust. The death toll from the Thirty Years War was proportionally double that of World War I and in the range of World War II in Europe (p. 142).