You're line of reasoning is way off base. You're trying to shoehorn a scarcity-based economy into a post-scarcity society. The idea of "contributing" (the way its currently thought of) will have to go away completely. Private ownership is a social construct. In a post-scarcity world our ideas of private ownership will have to change. Society will simply not allow the owner of Acme robot company to literally own everything (because he has a monopoly on labor). A more communal-based society will necessarily spring up. No one will stand for a monstrously imbalanced society.