The Moral Landscape as I read it, so here goes--first reactions.
Why do we need this foray into the nature of moral truth? Harris's explanation isn't quite what I'd been expecting. He says religious conservatives believe in big "T" moral truth, grounded in God's commands. That invigorates their pursuit of conservative policies, like George Bush's ban on new stem cell research. Liberals and academics are relativists who don't take moral truth seriously, Harris thinks. As a result, they're more wimpy champions of their own (more often correct) policy preferences. Harris wants to "start a conversation" about moral truth, and how it's really no different from scientific truth, and it's independent of religion. Thus, he hopes to bolster the liberal side of our society's moral debates.
If a shot of moral realism would bolster liberals, I'd get behind Harris 100%, but here's the thing--I think most liberals are already moral realists. Just read the op-ed page of the New York Times. Columnists like Maureen Dowd, Tom Friedman, and Frank Rich make moral pronouncements without hesitation, and with just as much fervor as Ross Douthat and David Brooks. They say it's right for there to be universal health care, right to prevent global warming, wrong to start a war by lying about WMD, etc. etc. Academics take stands on myriad moral issues, too, and emphatically. Like the vast majority of people, liberals and academics are "naive moral realists"--they're moral realists even though they never think about the nature of moral truth.
Harris might be confusing moral relativism with liberalism (in the philosophical sense). A relativist thinks there is no moral truth independent of...and now the view varies. The extreme relativist thinks there's no moral truth independent of each decision-maker. We each "make" a morality for ourselves. A cultural relativist thinks that moral truths exist for whole cultural groups, but don't transcend cultural boundaries. So for people in Saudi Arabia, it really is wrong for women to leave the house unescorted by a male relative, but for us it isn't.
Liberal political thought sometimes sounds a bit like relativism. Justice, on a liberal conception, requires (among other things) that everyone must have the liberty to pursue their own vision of the good, their own "plan of life." Laws and institutions have to leave it to citizens to make certain judgments for themselves. That's "to each his own"-ish, so sounds a little like relativism, but no: if you say "justice requires this...period" you're no relativist. In fact, you could think there are truths about the good life, and truths about the rightness of many actions and choices. As a liberal, there will simply be areas of life in which you think the individual ought to be sovereign.
Here's the interesting thing. Liberals are typically at their most confident when they say superficially relativistic sounding things, like that each woman should think and choose for herself about abortion, and people should have freedom of speech, and gays should decide about their own lifestyles and relationships. Are they less passionate in defense of individual liberties than religious conservatives are in defense of what they think God wants? Well, that's an interesting claim, but let's not just say it. I'll believe it when I see the empirical evidence.
Is Harris all wrong then? Are liberals in no way real relativists, whether cultural or extreme? Here's where I think Harris has a point: when liberals think about other cultures, they sometimes want to extend to them the same "personal autonomy" they think each individual is entitled to--effectively equating groups and persons (which is problematic). So some will accept Saudi Arabia's policies on women, in much the way they might accept an individual American having an abortion or a gay relationship.
But even here, it's simplifying too much to say this hands-offishness must come from relativism. Apart from card-carrying anthropologists, most of us (us liberals, that is), do make judgments (and should--I'm all for it), but try to make them cautiously, and open-mindedly, and without knee-jerk "we know best" ethnocentrism. They also think that interference, as opposed to mere judgment, is usually unwise. We should step in when the worst human rights abuses are involved, and when we can do so non-violently, and after forming the proper alliances. In other words, it's OK for Greg Mortensen to build schools for girls in Afghanistan, because he builds local support for the schools, and does the work non-violently. But it wouldn't be OK for us to invade Saudi Arabia to liberate the women.
So I think Harris is wrong to think liberals need to be saved from their own disempowering relativism, which is for the most part really their belief in personal autonomy--which they believe in passionately; and their reluctance to impose American ideals on the rest of the world mindlessly, and with force. But that doesn't mean we don't need Harris's book. It's useful to to think about what right and wrong are based upon--that's got to help us avoid moral error and get our hands on more moral truth. So...on with the book.
(Jesus, it's #3 at Amazon!)