Sam Harris is attempting to offer a "scientific" explanation for morality. He's responding to the grounding challenge for naturalism - where do moral values fit in a purely material, physical world? This is a significant challenge for naturalism and atheism since morality is something human beings universally know is real. So any worldview has to be able to account for it or else it's a fatal flaw of that worldview. Harris attempts to explain how science can account for moral values.
In this call from a recent radio program, Greg explained some of the fundamental flaws in Harris' account. The first step Harris makes is wrong - he identifies the mind as the brain. But as Greg points out, minds and brains have different properties, so they can't be be the same thing. Harris asserts this and then Harri's explanation suffers from circular reasoning. Greg explains.