Is this really about fairness?

IDK, but I have heard people refer to fairness in similar situations, so I am merely adopting their usage.

Seems like different people agree that fairness is a good thing, but use different definitions of fairness. Or perhaps the word fairness is often used to mean "applause lights of my group".

I agree. To a large degree the near universal preference for "fairness" in humans is illusory, because people mean mutually contradictory things by it.

For someone fairness means "everyone has food to eat", for another fairness means "everyone pays for their own food". Then proponents of one definition accuse the others of not being fair -- the debate is framed as if the problem is not different definitions of fairness, but rather our group caring about fairness and the other group ignoring fairness; which of course means that we are morally right and they are morally wrong.

I believe "fairness" can be given a fairly rigorous definition (I have in mind people like Rawls), but the second you get explicit about it, people stop agreeing that it is such a good thing (and therefore, it loses its moral force as a human universal).