I think you misinterpret collective rationality, as Weirich never try's explain a historical progression for western morality.
And as mentioned there have been other cultures with strong rational traditions that have come to far different moral conclusions than today - e.g. soviet/communism, Islamic societies,etc.. Pure reason thought doesn't go one direction, it can take you to very different and uncomfortable places.
And as mentioned there have been other cultures with strong rational traditions that have come to far different moral conclusions than today - e.g. soviet/communism, Islamic societies,etc.. Pure reason thought doesn't go one direction, it can take you to very different and uncomfortable places.