Does science have anything to tell us about the nature of morality? Could use of the scientific method help us apprehend the nature of good and evil? Sam Harris certainly thinks so as he appeals to the burgeoning field of neuroscience as the pathway to discovering objective moral facts. For example, Harris recasts classical virtues like kindness, willingness to follow evidence, and patience as “forces” of the brain that further the end of human cooperation. If such forces result in human well-being, then we ought to cultivate them to maximize human well-being, and ignore or destroy those that abate it.
The one virtue of Harris’s book is that it forcefully makes the case for moral realism. He admirably shares the concern of many, primarily those of religious persuasion, that atheists and scientists tend to slide too easily into moral skepticism. Its easy to see why he is so beloved by nonbelievers as his sharp wit and punchy tone make him someone you like having on your side. Being on the receiving end of his ridicule is no pleasure as he is adept at making any position he dislikes appear ridiculous. Of course, his rhetorical skills carry him only so far, and are useless when shouldering the burden of proof.
It seems that his argument could be summarized like this:
 Good and evil depend on the experience of conscious minds.
 Conscious minds are natural phenomena.
Therefore, good and evil can be understood through science.
Harris then describes “the moral landscape” as a space of real and potential outcomes whose peaks correspond to the heights of human well-being, and whose valleys represent the horrors of human suffering. A scientific account of human values is one that measures the outcome of world states and correlates them with the outcome of brain states. This makes Harris a consequentialist and places him squarely in the utilitarian tradition of John Stuart Mill who labored to give a qualitative account of the kinds of goods at play in the maximization of human happiness.
This is where things get dicey. By favoring the good of the many over the one, we are brought into conflict with doing good for those closest to us and doing good for those we have no connection to. For example, money saved by a parent for her child’s future college education could be spent on charitable giving to thousands of illiterate girls in Africa. It is therefore “wrong” to waste such vast resources on the education of one at the expense of the many. A consistent consequentailist might bite the bullet here, but things get more difficult if she had to choose between providing for her own hungry child and another one who is unknown to her. Perhaps, it could be determined that helping one’s own and helping those closest to us produce the best consequences in the long run. But that, as Bernard Williams famously put it, is one thought too many. We don’t help one’s own because it produces the best consequences. We do it because it is the right thing to do.
On the matter of justice, Harris thinks the only thing wrong with injustice is that it is bad for the conscious well-being of others. But surely this is too restrictive. Gilbert Harman’s “Room 306” thought experiment can be revised to eliminate conscious experience from Harris’s moral calculus:
You have five patients in the hospital that are dying, each in need of a separate organ. One needs a kidney, another a lung, a third a heart, and so forth. You can save all five if you take a single healthy person and remove his heart, lungs, kidneys, and so forth, to distribute to these five patients. Just such a healthy person is in room 306. The patient in 306 has been in a coma for five years and shows no signs of coming out of it. Being familiar with his test results, you realize that he has the right tissue compatibility with those waiting for organ donors, something that has been problematic for each of them getting a transplant. If you do nothing, the patient in 306 will persist in his comatose state for an indefinite amount of time while those in need of transplants will surely die in the very near future. The other five patients can be saved only if the patient in 306 is cut up and his organs distributed. In that case, there would be one dead and five saved.
Such action would be a clear instance of injustice even if the comatose patient has no conscious experience of the violation of his person (which is ultimately relevant). If the Dr. acted in secret and successfully covered his tracks, then he alone would be the only agent to have a conscious experience of his actions. Yet being a utilitarian (not to mention a psychopath) he senses no injustice, because his actions benefited the many over the one. Certainly, it is possible for him to come to regret his actions later, but it is implausible to suppose that at this later time injustice would then supervene.
This brings us to the most devastating problem for Harris’s “moral landscape.” Consider the following argument:
 If the property of moral goodness is identical with the property of neurobiological well-being, then one inhabits the peaks of the moral landscape when and only when one experiences neurobiological well-being.
 Moral saints experience neurobiological well-being when they help others.
 Psychopaths experience neurobiological well-being when they harm others (this much is admitted by Harris).
 Therefore, moral saints inhabit the peaks of the moral landscape.  and 
 Therefore, psychopaths inhabit the peaks of the moral landscape.  and 
 Yet it is possible that  and  are incompatible.
 Premise  violates the necessity of the law of identity stated in 
 Therefore, the the property of moral goodness is not identical with the property of neurobiological well-being.
This seems fatal to Harris argument.* If psychopaths and moral saints can exist on the same moral level, then morality is meaningless.
Other defects in the development of Harris’s account are too numerous to expound. His treatment of epistemology, moral responsibility and the philosophy of science are are riddled with errors and too crude to take seriously. His chapter on religion amounts to nothing more than a attack on Francis Collins that is utterly irrelevant to the rest of the book. It seems as though the author cobbled together a number of unrelated articles that were more or less written independently of one another. If one is looking for a robust defense of the idea that objective morality can be known on the basis of a naturalized epistemology, one will have to look elsewhere.
*The above, or something like it, went unaddressed in a debate with William Lane Craig (starting at 2:16).