Confucian ren was directly challenged by Mozi, the fifth-century BCE philosopher, whose doctrine of jian ai, impartial or universal love, argued that the graded, relationally structured love the Confucian tradition took for granted was itself the root of the era's chaos.
Confucian ren, as developed by Confucius and Mencius, is explicitly graded: one owes more to parents than to strangers, more to one's ruler than to a foreign state, and cultivation proceeds outward from the family in expanding but weaker circles, a structure Mencius defended directly against Mozi's alternative, arguing that a love making no distinction between one's own father and a stranger's father was effectively "no father at all," collapsing the special obligations that make family and society function. Mozi's jian ai proposed that people regard other states as their own and other people's parents as their own, holding that the partiality built into graded love produces the mutual aggression that plagued the Warring States period, and that only impartial concern for everyone's benefit could break the cycle.
The two sides argued past each other in a way later Chinese philosophy found instructive: Mencius treated Mozi's proposal as psychologically impossible, since a love spread with true impartiality struck him as no longer functioning as love at all, while Mohists treated Confucian partiality as morally arbitrary. Mohism as an organized school did not survive the unification of China, while Confucian graded ren became imperial orthodoxy, but the argument recurs in modern ethics' own debate between partialist theories permitting special obligations to family and impartialist theories, notably utilitarianism, that echo Mozi's insistence that everyone's welfare must count identically.