In his influential Theory of Justice John Rawls speaks of a "difference principle," a way of legitimizing social differences. He imagines people in "an original position" in which they do not know their ultimate social positions.
It can be hard to keep up with Marva J. Dawn, since she usually produces a book a year. But this one should definitely be on your reading list. Perhaps because Dawn has a new publisher, this book is crisper and more concise than her previous works.