"As you point out, even the most unskilled worker on the production line expresses that labour value of all the hours that go into rearing a person to adulthood too. Its the same principle. except that everyone has to be reared through childhood, so the differences in value are more subtle."
I utterly reject this. Life is not an achievement contest. No one has more value than anyone else. An hour of my life is worth an hour of your life. That's the only sane basis for an economic-social system. Everything else devolves into self-justification contests, is a waste of time, and reinforces the worst aspects of being a verbal and calculating being.
An hour of my life is worth an hour of yours, and we support whoever for whatever reason can't work. If you keep it simple, it may even be doable.
Joanna