Sam Harris is a liberal I respect and admire. He has not succumbed to the PeeCee delusion and he actively combats it. Although Harris is a contemporary, he is not a 'contemporary liberal' as I use that phrase: he is a classical or old-time or paleo or respectable liberal. But on religion and some philosophical topics he is out beyond his depth.
Here is Harris in his mainly excellent Sleepwalking Toward Armageddon (emphasis added):
And just like moderates in every other religion, most moderate Muslims become obscurantists when defending their faith from criticism. They rely on modern, secular values—for instance, tolerance of diversity and respect for human rights—as a basis for reinterpreting and ignoring the most despicable parts of their holy books. But they nevertheless demand that we respect the idea of revelation, and this leaves us perpetually vulnerable to more literal readings of scripture. The idea that any book was inspired by the creator of the universe is poison—intellectually, ethically, and politically. And nowhere is this poison currently doing more harm than in Muslim communities, East and West. Despite all the obvious barbarism in the Old Testament, and the dangerous eschatology of the New, it is relatively easy for Jews and Christians to divorce religion from politics and secular ethics. A single line in Matthew—“Render unto Caesar the things that are Caesar’s, and unto God the things that are God’s”—largely accounts for why the West isn’t still hostage to theocracy. The Koran contains a few lines that could be equally potent—for instance, “There is no compulsion in religion” (2:256)—but these sparks of tolerance are easily snuffed out.
Why does Harris think that the idea of divine (scriptural) revelation is intellectual, ethical, and political poison? Perhaps his reasoning is along the following lines.
1. In every extant scripture there are morally offensive prescriptions and proscriptions which, if followed, would be detrimental to human flourishing, and in that sense 'poisonous.'
2. If one believes that a given scripture is the Word of God, then one believes that everything in that scripture carries divine sanction (approbation): it proceeds from the ultimate moral authority in the universe.
3. If one believes that everything in a given scripture carries divine sanction, then one believes that one has an obligation to commit some morally offensive actions, namely, those enjoined in the scripture in question, actions detrimental to human flourishing. (from 1+ 2)
4. Actions detrimental to human flourishing are 'poison.'
5. The idea of divine revelation, if accepted, is 'poison.' (from 3 + 4)
I have just imputed to Harris an argument the reasoning of which is correct. Please recall the Logic 101 distinction between correctness/incorrectness of reasoning and truth/falsity of premises and conclusions. (If this argument, or something very similar, is not the argument at the back of Harris's assertion, then I have no idea what that argument would be).
But no defender of divine revelation need be troubled by the above argument. For such a defender may simply deny premise # 2. If a given scripture is the inspired Word of God, that doesn't change the fact that it is written down by men -- and we know what they are like: fallible, sometimes foolish, liable to embellish and distort, biased, limited in ever so many ways.
To put it very simply, I can accept a scripture as divinely inspired while rejecting parts of it as merely human accretions. Why not? There are things that St. Paul says, for example, that are pretty obviously nothing but reflections of his own personal preferences and biases, or else those of his time and place.
Notice that Harris is attacking the very idea of divine revelation: the acceptance of that idea is 'poison.' But he has given us no good reason to accept this wild claim. Of course, if there is no God, then there cannot be divine revelation. But the existence of God is not at issue here. The above argument is logically independent of the existence/nonexistence of God. Indeed, a theist could deploy the above argument.
And the issue is not whether particular portions of some scripture are credible or not. The issue concerns divine revelation as such and in general.
Harris may be assuming that anyone who accepts scriptural revelation must be a fundamentalist in the sense of someone who believes that everything in the Christian Bible, say, wears its meaning on its 'sleeve' and is literally true. But obviously, not everyone who accepts scriptural revelation need be a fundamentalist!
So much for the second of the two bolded sentences above.
The first sentence reads: But they nevertheless demand that we respect the idea of revelation, and this leaves us perpetually vulnerable to more literal readings of scripture. This sentence encapsulates an inference which, unfortunately for Harris, is a non sequitur. If one respects the idea of divine scriptural revelation, how is it supposed to follow that one is vulnerable to literalism? It obvously doesn't follow. And what exactly is literalism?
Harris ought to read Augustine on the interpretation of Genesis. Here is a sampler of some of the issues that arise.
As I said, Harris is way out of his depth when he enters these theological waters.