If God's word exists, it does so in nature and natural processes. Humans have a core morality that developed millions of years ago, before Homo sapiens, an adaptation to survival in an environmental filter letting through niceness, cooperation and communication. At any given generation, there is variation in the degree to which individuals lie along the core morality distribution curve, not always Bell's shape. Some terrorists and moral monsters, some ultra pacifists and saints.
"[F]anatical zealots" behave irrationally differently than most of us do because they're farther away from the average core morality.
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