Let's not conflate cost and value here. The price people pay for my blood is at least the value to them. The same goes for my labor. I'd say the buyer gets a

Let's not conflate cost and value here. The price people pay for my blood is at least the value to them. The same goes for my labor. I'd say the buyer gets a greater value per dollar paid from my lifesaving blood than they do from my relatively mundane laboring. By that reasoning I'm more valuable as spare parts, not less. The implication of the calculation isn't nearly as sweeping as you think, it's merely that more people should donate blood. Especially if it has low "cost" to them compared to others (say, because they're not queasy about it). Given what we know about what people are willing to pay for both, I think it's fairly clear what society values more. If an evil genie forced me to choose between reliving my life in a way that either deprived the world of my blood products or of my labor, and I knew that on the basis of money alone my blood was more valuable, then unless I was doing some particularly civic-minded work it would seem obvious I'd contribute more as an unemployed blood donor.