Looking at the rules for Sushi Go Party and the zero sum clause is kind of hilarious here. The concept of the game is that you're all trying to eat some really good sushi. But if your sushi meal isn't the best then you Lose. You Fail to Win The Evening at a Sushi Restaurant. The deliciousness of your friend's meal diminishes your own.
I am starting to get a sense of something sensical here, though. Assume the purpose of play is exploration of game system dynamics. Playing in an adversarial way reveals how much leverage we have over each other. If humans run on shapley values (which apportion proceeds from coalition agreements according to each player's leverage, regardless of whether the leverage would come from real contributions or from blackmail); your ability to injure others is a quantity that you would want to know
The thing is, given arbitrary contract enforcement, blackmail becomes impossible, afaict? Functional decision theory is immune to blackmail, supposedly, but I'd like to take a closer look at how, one day.