From the Code of Hammurabi to the Confucian concept of ren to the Ubuntu communal principle to Rawls's original position, every civilization that has examined the question of how to live together has arrived at some version of: do not treat others as though your interests are the only ones that count. The remarkable cross-cultural convergence on this principle — that some form of reciprocity or impartiality is the ground of justice — suggests it is not culturally arbitrary but tracks something real about what social life requires. The disagreements are in the details, which happen to be enormous.
Each step builds on the last.