This extremely unlikely situation hinges on profound wealth inequality. Only someone staggeringly, fantastically, mind-bogglingly rich (and also completely nuts) would blow 5 million on eating a human arm. And only someone who is really struggling in life would contemplate such a huge sacrifice for mere money. Since the actual variation in human ability, and therefore economic potential, follows a tame bell curve as opposed to the radically skewed distribution of wealth that this scenario requires (and that we actually see), this represents a market inefficiency. If we permit this transaction to take place, the economic potential of the formerly-armed takes a huge hit, while Cannibal Jeff Bezos does not enjoy a corresponding gain. Thus not only is the transaction negative-sum, but the inequality (and hence the inefficiency) is exacerbated.