The key point is "any other activity". For most people, the cognitive games on their phones are probably the most accessible enriched environment tools. The blood, on the other hand, seems to be fraught with complications, from basic health concerns to economic issues. The Red Cross is almost always calling for more donations to blood, I can't imagine the situation improving if richer people start buying the blood of younger people.
How about an organisation you can join where you donate your blood when you're young and receive blood when you're older?
Of course there can be problems in the long run (just like the German pension scheme has some), and it is necessary to create trust, but it's fairer than the outlook you present.
No, I meant that the young people donate for the old, and that once they turn old there will (hopefully) be more young people to donate blood, again to receive blood from other young people when they turn old. Kind of like a pension scheme (at least the one we have in Germany works that way).
