Sam Harris keeps up the fight:
As I argue in my new book, even if there are a thousand different ways for these two people to thrive, there will be many ways for them not to thrive--and the differences between luxuriating on a peak of human happiness and languishing in a valley of internecine horror will translate into facts that can be scientifically understood. Why would the difference between right and wrong answers suddenly disappear once we add 6.7 billion more people to this experiment?
Granted, genuine ethical difficulties arise when we ask questions like, "How much should I care about other people's children? How much should I be willing to sacrifice, or demand that my own children sacrifice, in order to help other people in need?" We are not, by nature, impartial--and much of our moral reasoning must be applied to situations in which there is tension between our concern for ourselves, or for those closest to us, and our sense that it would be better to be more committed to helping others. And yet "better" must still refer, in this context, to positive changes in the experience of sentient creatures.
I haven't read the book and will, because Sam is both a friend and a brilliant man and I have learned and benefited from both his last books. But in discussing this book's arguments with him a while back, I found myself making many of the same points Kwame Anthony Appiah makes here. Utilitarianism - the search for morality grounded in pure well-being - is not new in the world of ideas. But its premises remain thoroughly debatable and the notion that these eternal questions can at some point be empirically or scientifically resolved is, to my mind, a category error, an ignoratio elenchi.