To anticipate a possible counter-objection on this topic, which might attempt to dismiss the concerns of philosophers (such as Hume, Kant, Rawls, and Mill) regarding the topic of the is/ought problem as being perhaps obscure philosophical wanking (which I have sometimes seen likened to religion or theology) it is not a matter of counting the numbers of angels on the head of pins. This is the core issue in any discussion of morality: how do you argue that your individual views about right and wrong are not merely your opinion but are fact? Kant tries to do it with an extremely clever formulation of the golden rule.(1) Mill tries to do it with some ham-fisted handwaving about maximizing the common good(2) and Rawls makes some brilliant game-theoretic leaps to try to overcome the flaws in Kant’s categorical imperative(3).
We humans seem to limp along without an objective morality, basically surviving in societies in which self-interest is the norm and there’s a constant struggle for power – not justice: power. It seems to me that the search for morality is silliness; it ought to be pretty clear that all attempts to establish an agreement in principle amount to nothing more than reifying one person’s opinion as “right” – usually the person with the biggest stick. Harris fails to start with moral nihilism as his default position and to move from there probably because he doesn’t really understand what he’s doing. He’s not really very well-educated when you come right down to it.
(1) Imagine that the world you live in is the world in which everyone acts as you do; therefore you should act well. Objection: this is obviously simply Kant’s opinion; we can see that selfishness exists and therefore Kant is simply projecting his moral sense onto others.
(2) Objection: how do you know your idea of what the common good is is fact and not merely your opinion? I.e.: “the common good” presupposes you have a working morality, which is begging the question.
(3) Imagine that you construct the world you will live in, with no advance knowledge of your place in it; the argument is that a rational person will create the most fair world possible. Objection: this is actually an appeal to self-interest hidden behind smoke and mirrors; if you’re willing to assume that self-interest is the basis for morality you’ve actually scored an own-goal.