I agree that as long as any ethic is based on a belief, accepting it is a matter of personal predilection only. If anyone rejects a belief, it can only be imposed on that person one way or another.

I thought this author might find interesting an ethic that follows from an empirical observation, involving no belief. That observation can be verified by any human being. Therefore, the ethic following form it is not being imposed on anyone.

The observation is that human beings have no choice but to effect choices. That makes choosing integral to being human. To recognize one another as fellow humans we must respect the capacity of others to choose for themselves--beginning with choosing whether/to what extent to be involved in the process whenever any choice is being effected. So the 'ethic of justice' is mutual respect in effecting choices. As the ethic of justice, both its determiners and its referents are contained within material existence.

To act otherwise is to assert a claim of some relative status among the beings involved that cannot be empirically verified. No one can be under any compunction to accept the validity of any such claim. That applies to any belief.