Check out Plato's cave.
These people are told from an early age what to believe and when you lead them out of the cave (ei enlightenment with atheism) they would rather go back into the "cave" of religion and believe a simple lie.
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The cave isn't specifically speaking out against religion, it's speaking against religion, government, and blindly following the opinion/status quo of the masses. Idk why people still do religion, maybe they feel it's one of the last sources of "power" they have control over.