I disagree -- I think unfairness is about morality, and in many of these conversations people often conflate inequality with unfairness.

A perfectly equal society can also exhibit a great deal of unfairness, and a perfectly fair society would most likely be unequal.

"Fairness" should be the metric under discussion, not inequality.

Definitely morality, but also the stability of a society. The provision of the good life to the people, etc.