"There's no wrong or right, but I'm sure there's good and bad."- Eddie Vedder
Sam Harris will certainly dwarf William Craig in the history of important thinkers, but Craig strikes an undeniably clean victory in this particular debate. Craig cheats a bit, by ignoring the whole "Why can we presume God exists?" thing and focusing on the syllogism that: If there is no God, then there is no basis for objective moral responsibility. Since Craig speaks first in the debate, Harris is compelled to respond to this opening salvo. He does not shy away from this ultimately less important line of reasoning, but he repeatedly fails to overcome Craig's logic.
Perhaps the reason that Harris is such an non-theist's dream-boy is also the reason his occasionally transcendent-ish approach to human existence never holds quite as much water as crotchety uncle Dawkins. While Dawkins doesn't really fire the imagination quite like Harris, his game is all about being as reductive and 100% cogent as possible. This makes him the essential skeptical figurehead. But Harris is more futuristic and captivating; he indulges the poetry of logic. His forward-seeking ideas attempt to reconcile the human spirit with its quantum scaffold. He frequently terrifies and sooths, and ultimately presides a marriage of neurology with philosophy that awakens within the tattered, tired, casual skeptic the youthful bliss of discovery. In this debate, he does a very good job of convincing that--even in lieu of objective moral value--there is plenty of reason to strive for "good", as we all pretty much understand it.
But still.. at the end of the day, he does not persuade that objective moral value is a thing.
This is always a big dilemma for non-theists because the justification of one's own personal agency against a back-drop of eternal "who-gives-a-shit" can seriously deflate the sensation of experience and amplify what Kierkegaard called "the dizziness of freedom". A frequent argument by theists states "why would you want to live in such a horrible, horrible universe with no objective moral value? I've even heard atheists use this same argument--I wouldn't WANT to live in a universe where a vengeful, murdering God robs us of personal dignity. I think Duane "The Rock" Johnson would remind us that the whole purpose of seeking extrinsic truth is... "It doesn't MATTER what you think would be a better universe!"
Sam Harris is idealistic, which is important because he may someday be able to prove the existence of objective moral value. It would be an mind-blowingly important discovery, a mere half-step down from the discovery of God himself. But if we are agreeing that science is the highest mode of knowing, he needs to realize that he has not done this yet. The thought experiment he posits suggests that if we can imagine a world in which we can inflict the ultimate suffering on another being--the most suffering possible--the contrast against a flourishing scenario with the least suffering possible makes it impossible to make the wrong decision. The objective good, in this example, becomes obvious.
But Craig points out, quite simply, this "obvious choice" is merely preferential to the experiential agents involved. If Nazi's won the war, he explains, and managed to successfully convince the surviving population that their elimination of the Jewish people was a good thing, there would be no experiential agency to say otherwise. Basically, Harris' obvious choice is merely a common opinion, and not an objective moral value.
At the end of the day--or until he or some other rock-star scientist or lingual gymnast proves the existence of objective moral value--Harris needs to realize that preference for flourishing over suffering is simply a groovy, mammalian fetish. I watched his Ted Talk on this very topic after writing most of this, secretly hoping that I'd have to delete it all because he cracked the code, but he hasn't. He proves that science can prescribe best-case-scenarios for lots of issues having clear, communal preferences. But he can't get suckered into this common tease that a universe with no God is pretty much the same as a universe with God.
(On second thought, it's almost suspicious that flourishing seems to have been selected by the universe as the road to evolution and discovery. If the purpose of life is for the universe to discover itself, then is flourishing by definition an objective moral good, or just a means to an end? It's unsettling that chimpanzees defeated the bonobos in the evolution race using biting and strangling. Perhaps the bonobos' pansexual toddler-stasis was pre-maturely indiscriminant. Perhaps existence is less a canvas and more a sculpture. Perhaps suffering is shapelessness and we chromosome puppets are called by the essence of characteristic to move towards form?)