Rationale for organ donation: charity or duty?

Media appeals encouraging people to sign organ donor cards suggest that donating one's own organs after death or donating the organs of a deceased family member is an act of charity, i.e., something which it would be meritorious for people to do but not wrong to avoid. This paper argues to the contrary that posthumous organ donation is a moral duty, a duty of the type that rests at the base of recently enacted state "Good Samaritan" laws which require a witness to an emergency situation to render aid to the victim(s) when this can be done at minimal cost/risk to the potential rescuer.