I think you misinterpret collective rationality, as Weirich never try's explain a historical progression for western morality. And as mentioned there have bee

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.