A zero sum-game.
Funny you should say that. We used to have a poster here (no need to mention names!) who justified all commercial activity, for its own sake as a zero-sum game. He would glibly pronounce: "No one put a gun to their heads and made them buy it." "The reason the system works is that it IS a zero sum game." Both buyer and seller benefit equally. "Its all about 'Supply and Demand'; the Fundamental Law of the Universe."
I paraphrase, of course. And the emphasis is my own. But I can't help it if that's how my filters are tuned.