Having followed the release of the book and some of the debates surrounding it I felt obliged to dutifully familiarize myself with the material if I wanted to engage in the discussion in good faith, and so I have.
Near the beginning of The Moral Landscape Harris identifies two groups of individuals who he knows will take issue with the argument he intends to present. On the one hand there are religious people who believe that moral values have a transcendent source and orientation and that therefore science can't investigate moral claims. On the other hand there are secular intellectuals, the majority of whom accept David Hume's articulation of the is/ought problem and who therefore also reject the notion that any 'is'--any fact or set of facts--can be prescriptive with regard to human duties or values. Both groups would object to the notion that, as the subtitle of this book claims, 'science can deterimine human values'. But that is what Harris intends to demonstrate--or at least assert.
Harris' argument ends up largely being that once human values are known or given, science can then reveal better and worse ways to go about achieving those ends. Notice that this argument is markedly different from the claim of the subtitle of the book. Using sleight of hand Harris attempts to pass off science's ability to evaluate a given value for its ability to determine a value.
Harris effectively presupposes that human (or creaturely) well-being is the pinnacle of conscious experience and that misery and suffering are the valleys. He acknowledges that these values can't be arrived at empirically or by means of brute reason, and therefore he essentially admits that the subtitle of his book is false.
While the subtitle of the book was particularly irksome to me for this reason, once you get past that issue the book really wasn't too objectionable for me as a Christian reader. I imagine that Harris thinks many of the things he's saying are anathema to religious persons, but most of what he says either accords with orthodox Christian theology just fine, or at least isn't opposed by it. Harris wants to affirm the existence of 'objective' moral values and so do Christians; we just don't believe such a thing could exist if atheism were true.
In his work as a neuroscientist Harris makes what were, for him, some surprising discoveries, but which wouldn't surprise a Christian. For example, he did an experiment where he neuroimaged the human mind while it was shown statements of widely varying content and characteristics. To his surprise the statements "2+4+8=14" and "It is good to treat your children with love" registered as the most similar in the human mind, despite seeming to be the most different in nature. Again, to the Christian who believes that the human mind is a divine product, and that morality is as much a matter of fact as math, this is exactly what we would expect to find. To Harris this signified that the fact/value gap might not exist at the level of the human mind, contrary to what most secularists maintain. Just so.
Harris' argument that science--the study of God's material creation--can reveal moral truths is hardly surprising for the Christian as Christian doctrine has long affirmed just that. The point that religious people and secular philosophers alike often make is that without some transcendent source a fact can't determine a value. Harris is assuming a priori that there is not a transcendent source, observing in his research a mingling of facts and values, and then when confronted with this intractable logical problem he simply brushes it aside. This has the curious effect of rendering Harris' worldview more in sync with reality as it is--with how God made it--but incompatible with atheism; while his nihilistic, atheist philosopher opponents are more logically consistent given atheism as a presupposition, but their worldview doesn't accord as well with the empirical findings of neurobiology. You can have consistent, nihilistic atheism; you can have consistent, moral theism; you can not have consistent moral atheism, and nothing about Harris' project confronts this unavoidable reality.
Which is not to say that he is unaware of the objections, he just finds them trivial and dismisses them, when in reality they are fundamentally problematic for his entire enterprise. The problem is not his claim that science can evaluate or even determine human values, but that it can do so and atheism can be true. Both his religious and secular critics have it right, and the long held philosophical basis for this conclusion is sound and Harris offers no counter to it.
Christians can happily affirm that science reveals some basic moral truths, with the caveat that the Bible reveals the same truths with greater accuracy and precision. The latter is what Harris would object to, I assume, but he offers no argument that Christian morality necessarily contradicts the moral truths that a scientific study of nature reveals. And since he spends so little time attempting to show that this is the case, a Christian should have very little fundamental reason to object to the content of the book--although one can point out that the content is incoherent coming from an atheist.
When he does talk about 'religion', and how it is in moral opposition to science, he talks about it in general and abstract terms rendering his observations either vacuously true, or often simply false. For example:
Because most religions conceive of morality of being obedient to the word of God (generally for the sake of receiving a supernatural reward) their precepts often have nothing to do with the world.
Even if this were true of religion in general (which I don't even believe that it is), it is certainly false with regard to orthodox Christianity specifically. Christian moral law is not arbitrary, but revealed to humanity for human's own sake, and primarily for their own sake in the material, created realm. This renewal and salvation of this material world, of the flesh of the sinner, is what the Gospel is ultimately about. The Gospel of Christ is certainly not about following moral law to earn supernatural rewards, that is merely a simplistic caricature of faith that exists in Harris' mind (and unfortunately in the mind of some fundamentalists as well).
Further he affirms that it is morally encumbent upon humans to avoid certain 'natural' tendencies. Again, this does not make much sense given his presuppositions, but it is entirely consistent with the Christian conception of morality.
Evolution may have selected for territorial violence, rape and other patently unethical behaviors as strategies to propagate one's genes--but our collective well-being clearly depends on our opposing such natural tendencies.
The book goes on to expend much of its energy toward fighting against moral relativism and, again, should be applauded for doing so. Harris aptly points out that moral relativism is a self-contradictory position. He also makes a sound case against the pervasive cultural relativism that says that since morality differs from culture to culture, one culture has no right to denounce another's moral code as inferior. Harris rightly argues that this isn't the case and that since we can identify cultures that are more adept at creating conditions conducive to human flourishing, as well as those with values that are remarkably efficient at ensuring high degrees of misery, we can make objective judgments about the values and practices of various cultures with respect to the goal of maximizing human well-being. I would mostly heartily agree with this. Although I would also point out that merely reading the Bible is a shortcut to arriving at the same conclusions of a 'science of human well-being'.
A very curious feature of the book is the chapter on free will in which Harris asserts a deterministic worldview, which he claims science confirms almost necessarily, in which free will can't exist. His argument is, as should be expected, highly inadequate and unconvincing. And this, I should remind you, comes directly after he has already affirmed the existence of a kind of objective morality. He again admits that this presents a bit of problem for moral accountability, but he doesn't seem to grasp just how enormous the problem. After all, what sense does it make to declare the virtue of a particular science-based morality only to cut your own feet out from under you? If free will does not exist then morality is an illusion.
In this section he asserts that neuroscience leaves little room for a soul in the sense of a 'ghost in the machine'; an immaterial causal 'substance'. Again, apparently oblivious to the fact that very large portions of Christianity reject a 'hard' dualism of this sort, and instead affirm that the soul is not in any real sense 'separate' from the body or mind. As is typical for writers in this genre, he constructs arguments that might be problematic for particular brands of religious fundamentalism, but not for religion in general and certainly not for orthodox Christianity.
It seems to me that few concepts have offered greater scope for human cruelty than the idea of an immortal soul that stands independent of all material influences, ranging from genes to economic systems.
If we grant this somewhat dubious observation to be true--which we aren't obligated to do--it has little relevance to the Christian faith which holds that the soul does not stand independent of all material influences, but instead that the actions we take in this world affects the soul, and the soul in turn has the ability to affect the world. The Straw Man cometh.
While Harris lodges some legitimate arguments against a hard mind-soul, or body-soul dualism, he imagines that he is striking blows at the heart of religion or Christianity themselves, when he is doing no such thing.
As a screed against the pervasive moral relativism or nihilism that exists in academia The Moral Landscape is a compelling book that makes a strong argument. As a screed against religion or orthodox Christianity it's comically irrelevant and inept. As a coherent moral philosophy, consistent with the author's atheism, it fails rather spectacularly.