Look, of the people collecting my blood are turning around and selling it for a lot of moeny, shouldn't I get some of the money? That's all folks are saying. I agree people should want to do it to be a good citizen to their fellow humans, but the people getting the blood should also not be making money off of it in that case.
So if the answer to "How much is blood worth?" is "Nothing!" Then awesome! If the answer is "A lot, actually..." Then something is wrong.