Sure, but much of the fairness we argue about as adults is due to fundamental disagreements about morality or how the world should work. “It’s not fair that tax cuts benefit the wealthy.” Republicans think it’s not fair to take money from people who earned it. Democrats think it’s not fair for some people to have more wealth than they’ll ever use while others have so little. But the concept of “fairness” doesn’t do anything to help us resolve that disagreement.

But at the same time, there are some aspects of fairness that do appear to be innate - as in, they're observed in very small children regardless of the culture they're from, in experiments where they're asked to share (or not share) something that they have, or assess how someone else shared theirs. Extreme "wealth inequality" - as defined, say, through the amount of candy each child has - is universally seen as unfair, for example, although you also have to account for parochial altruism. Bonobos also demonstrate similar attitudes.

So it appears that our evolution as social species has set some hard boundaries. Abstract ideologies can go beyond them, of course, but their real-world success seems to correlate to some extent with how much they do or not - I would argue that ancap definition of "fair" is so unpopular precisely because it's so out-of-bounds wrt our biology.

It doesn't need to help us resolve the disagreement to be useful to explain why the disagreement is there in the first place, though.

And, in practice, there are large groups of people who do share the broad definitions of "fairness", and therefore saying that something is fair or unfair is useful to communicate the idea within those groups. This is not something that people really like to see put quite so explicitly, but when we say something "this should not be so because it is unfair", it carries an implicit "... and I don't care what those who disagree with me about what 'unfair' means think".