Enough barely-worth-living lives can outscore a small thriving population

Derek Parfit showed that if you value a population by total wellbeing, a modest group living wonderful lives can always be beaten by an unimaginably larger population whose lives are each barely worth living, since the sum still comes out higher. Almost everyone finds this repugnant, yet Parfit couldn't find a rule for comparing populations that avoids it without creating other problems.

— Derek Parfit, Reasons and Persons — Part IV, Oxford University Press, 1984
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