Well religion has been passed down through the years by stories people tell around the campfire. Stories about God stories about love. Stories about good spirits and evil spirits.
It appears to be in the nature of religion itself to be prejudiced against those who are different.
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Basically fundamentalism is a modern phenomenon. In the same way that Hitler evoked a mythological religion of German purity and the glory of the past the Islamists use religion to evoke emotions and passions in people who have been oppressed for a long time in order to reach their purpose.