Probably because it's meaning has been lost through time. Original sin is man's failure to take accountability.
Nothing silly about that. What's silly is how people read ancient man's answers to the origin question.
Original sin is the Christian doctrine that humans inherit a tainted nature and a proclivity to sin through the fact of birth. Theologians have characterized this condition in many ways, seeing it as ranging from something as insignificant as a slight deficiency, or a tendency toward sin yet without collective guilt, referred to as a "sin nature", to total depravity or automatic guilt of all humans through collective.......
Original sin - Wikipedia
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