What you're saying here is that "give them an inch and they'll take a mile" is not just a description of an unfortunate reality, it's a moral imperative. Give them an inch and they have a right to that mile.
Do you not see how totally destructive this moral framework is? If giving away free work instantly entitles anyone who benefits from that free work to an arbitrary amount of additional free work, the only rational move for a would-be contributor is not to play the game at all. Is that really the world you want to live in?