You need a background in NCE to grasp this point? That's odd. I accepted the view at the ago of 10 or so when my father (who has never taken an economics class and is now actually far to my left on most issues) explained it to me. However, I should point out that the view isn't unproblematic. Not all mutually beneficial arrangements are intuitively justified. Right now, one billion people live on a dollar a day (adjusted for purchasing power, of course). Suppose that I were to take one such person as my slave, and further suppose that I'm a kindly slave owner: I'll provide him with all the food he wants, pay for his medical care, and make sure that he has most of the day free for leisure. In many cases, such an arrangement could leave both participants better off than they would've been if they hadn't entered into it. Of course, one could protest that one party hasn't entered into the arrangement voluntarily, and thus it's wrong. But, as some German dude once tried to argue, wage labor doesn't always appear to be voluntary, either.
-- Luke