The question of a moral justification for any current economic process would indeed be incoherent or wrongheaded within economics. That's because economists fancy their discipline a science, so they're interested only in instrumental rationality, in means-end relations, not in the evaluation of goals. Of course, economics could still be morally evaluated from an external vantage point.

In any case, my point was about whether economists would find fault with the mechanisms of implementing your proposal. You say the mechanisms follow swiftly from the "rule." But whether the system would be sustainable is another matter.