Consider the game though. Imagine a basketball game where one team is getting away with fouls. If the other team starts doing it and gets called on it, they ca

Consider the game though. Imagine a basketball game where one team is getting away with fouls. If the other team starts doing it and gets called on it, they can't say "well I know we're doing it, but so is the other team." That exemplifies your point. Now consider "free" trade. There is no referee. There are no rules akin to the rules of basketball that each team agrees to. It is just two parties that are deciding what is in their own best interest. When one party feels like they have been cheated, why should they carry on as if nothing happened? How is that in their best interest? There are no overarching rules or governance which both parties are subject to. So "not stooping to their level" isn't going to be commended or rewarded by some party. It's like if you were playing basketball at the park and your opponent repeatedly fouled you but insisted fouls are legal. If you want to perform well, either you find a different team to play against or you start fouling back.