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Pierre Bayle, the great 17th-century French philosopher, had a bleak view of history: "Properly speaking, history is nothing but the crimes and misfortunes of the human race," he wrote, presaging a similar remark a century later by Edward Gibbon. Steven Pinker, in his recent book "The Better Angels of our Nature," reminds us that it took a long time for the victims of those crimes to be collectively noticed, mourned and remembered. Even if religions always cared for and honored the dead, it is only in recent history that we collectively commemorate the victims of the past. In modern social democracies, history has become, largely, the memory of the memory of "crimes and misfortunes" of the human race because remembering has become a moral duty, even a moral imperative. It is a moral...