Ophelia Benson is unswayed by Sam Harris's The Moral Landscape:
Harris spends most of the book hammering home the point that morality is about the well-being of conscious creatures, which means he spends far too little time considering the difficult questions that arise even if everyone agrees on that. He also frequently treats those questions as easily settled, for instance when he says, “I think there is little doubt that most of what matters to the average person – like fairness, justice, compassion, and a general awareness of terrestrial reality – will be integral to our creating a thriving global civilization and, therefore, to the greater well-being of humanity”.It's a fair criticism as far as it goes, but the exact same criticism applies with equal force to the moralities that claim to be founded on divine fiat: virtually all monotheists insist their god requires love, charity, and justice for all people, and yet we observe enormous gaps between the nobility of the precepts and how believers really behave everywhere we look. Christians recite the Sermon on the Mount on Sunday before liquidating others' livelihoods, paying themselves bonuses, and cheering wars by Monday morning. Muslims proclaim the infinite mercy of their god before and after decapitating people for offending him.
Almost halfway into the book he does suddenly admit the difficulty – “population ethics is a notorious engine of paradox, and no one, to my knowledge, has come up with a way of assessing collective well-being that conserves all of our intuitions”. He then quotes Patricia Churchland saying, “no one has the slightest idea how to compare the mild headache of five million against the broken legs of two…” Quite so, and this acknowledgement should have come much earlier and been woven into the discussion throughout. Because it isn’t, the first part of the argument seems much too quick and effortless. If it were that simple, the reader keeps thinking, why wouldn’t everyone just do it?
Harris spends most of the book hammering away at understanding morality in terms of the well-being of conscious creatures because the main alternative, divine command, is considerably more deficient -- it too doesn't give any prima facie guidance on deciding between the "mild headaches of five million against the broken legs of two," and any deeper adjudication would require precisely what we have persistently lacked, the explicit clarifications of the true god(s). Human beings have been arguing over god's "real" directives for all of recorded history and have yet to receive a definitive bulletin from the beyond the clouds. For every question there are countless answers even within creeds -- e.g., Catholics versus Lutherans versus Southern Baptists versus Christian Scientists versus Mormons versus literally thousands of other sects. Crossing the creed boundaries and adding more gods and systems only multiplies these difficulties.
Whatever its shortcomings, Harris's proposal lacks this problem. The impact of choices on the well-being of conscious creatures is, in principle and frequently in practice, subject to empirical investigation. This is a far better place to start to get answers summing up to anything worthy of being called a moral system.