This article seems to equate religion with the existence of civilization. Non-civilized peoples have definitely had religion in one form or another, to include a role in promoting ethical behavior.

I think we can divorce justice from morality in general. Justice is concerned with how we treat one another; morality can include purely personal matters such as thoughts, feelings, attitudes, etc.

I have become convinced that all human beings know intuitively that the ethic of justice is mutual respect: taking one another into account as we live our separate lives together in this world. All religions and philosophies that are concerned with justice recognize that ethic in one form or another.

I have shown (to my satisfaction, at least) that it also follows from the observation within material existence that we human beings have no choice but to effect choices. That makes choosing integral to being human. It follows that respecting one another's capacity to choose must be integral to our relations with one another. Thus, this approach to justice involves no belief of any kind, whether sacral/theological or secular/ideological.

There are many paths to mutual respect as the ethic of justice. We can think of it as the definitive, sufficient, prescriptive 'condition of justice', telling us how we must act to act justly. There is no limit to how justly a person might act.

In studying the matter I have found that there is a minimum, necessary, proscriptive 'condition of justice'. It tells us what we must refrain from doing to keep from acting unjustly. It boils down to a handful of absolute prohibitions: no killing, harming, coercing, stealing, or manipulating (which includes lying, cheating, etc.) in our relations with one another.

Those prohibitions apply to all people in all times, places, and circumstances. Anyone who is abiding by them is being just enough.