I am trying hard to let questions of epistemology rest for the time being in this space. However, responsibility demands that I link to Sam Harris's expanded thoughts on the subject of his TED talk.
I find his essay, while significantly more useful than his TED talk, to be something of a mess-- really unfold the logic of his supposed untangling of the problem of knowing a psychopath is wrong, even for a few minutes-- but again, I'm trying to let things rest. I'll just bring up one point: here, as in the TED talk, Harris insists on talking about moral questions of the highest possible emotional baggage. He also talks almost exclusively about issues which, whatever the larger epistemological questions, in the pragmatic context of our own lives, very few of us see as morally challenging. For someone so insistent on transcendent logic, I am deeply confused as to why he would make so many arguments that amount to a naked appeal to emotion. Harris is logician enough to know that saying "look into the eyes of a girl blinded by acid" is not logically compelling, and that harping again and again on emotionally charged issues is not the way to dispassionately pursue truth. (Capital T or otherwise.)
Probity and practicality would both suggest, it seems to me, that Harris concern himself with issues of actual moral controversy, ones that we have a great deal of trouble untangling-- abortion, euthanasia, torture in wartime, etc. The fact that he doesn't is troubling.