I’m not sure how this view of justice as mutual respect for beings that must make choices goes beyond liberalism. It sounds like the liberal’s point about the need for tolerance of those who are likely to express their freedom differently. These both make the point of humanism, which is that morality should be based on anthropology, or on an understanding of human nature.

There’s also the problem of the naturalistic fallacy. If your aim is to derive an ethic not from an arbitrary belief or ideology, which would be subject to “postmodern” skepticism, but from “material existence,” that runs into the problem that prescriptions don’t follow automatically from descriptions. There are lots of objective conditions of morality. Morality applies to people or perhaps to animals, which have certain natures. But describing the nature of the beings that are subject to moral evaluation doesn’t obviously suffice for the rightness of any value. The natural facts alone don’t dictate how we should evaluate our behaviour.

Indeed, it’s not clear that there’s any purely objective description of the natural facts which doesn’t add an “arbitrary” conceptual element, a generalization, simplification, or idealization, as in a model of the raw data.