墨子 Mòzǐ lived about a generation after Confucius and founded one of the first principled challenges to Confucian traditionalism. He and his followers, known in English as Mohists, advocated 兼愛 jiān ài, "universal love," the idea that policies should be set on the basis of what is in the best interests of everyone. In contrast to Confucius, who thought that the family was the source and the model for all human relationships and should therefor be given priority, Mozi was an egalitarian: everyone should count equally. Specifically, political policy should be set by what maximizes wealth, order, and total population, not just what is in the interests of the ruler. Their method for instituting this was a legal system that rewarded people for doing things that helped the world and punished them for doing harm. They were against offensive warfare and researched defensive technologies and techniques that would make attack unprofitable.
"Universal love" was not an emotional stance. Quite the opposite, the Mohists were ruthlessly pragmatic, discouraging things like expensive funerals and even music that they thought were a waste of resources. The later Mohists were so convinced of the reasonableness of their position that they thought that all that was necessary for it to prevail was an accurate description of the world and clear logic to deduce the consequences of any action. (See Graham's Later Mohist Logic, Ethics, and Science.)
The Mohists appear to have been a working-class movement. They frequently use metaphors from the crafts, for instance arguing that moral judgments need to have clearly defined criteria, like a carpenter's level, right-angle, and compass.
Mozi's followers were numerous and were among Confucianism's chief competitors, to such an extent that 儒墨, "Confucians and Mohists," became a byword for political bickering. Many later philosophers who do not present themselves as Mohists, including Zhuangzi, himself, were familiar with Mohist terminology and methods, suggesting to me that they may have flirted with Mohism in their youth only to become disillusioned with its methods, much like many college students with Marxism. For example, Huizi's final thesis in CTP 33.07, "Love all things like a flood; heaven and earth are one body," sounds like a version of universal love. I wonder if Huizi's monism and possibly even Gongsun Long's anti-dualism (like Parmenides and Zeno?) may have stemmed from an attempt to provide a theoretical underpinning to Mozi's ideas.
Graham says, "Although the impersonality of their writing makes it hard to imagine ourselves into their attitudes, one has the impression the Mohists were not people with warm sympathies towards everyone, but people whose personal affections are disciplined by a stern sense of justice" (Later Mohist Logic, p. 12). If, in fact, Zhuangzi were a follow of Mozi's in his younger days, this may be exactly the fault he is trying to correct. He rejects their rhetorical project of starting with an accurate description of the world since the world is inherently ambiguous; we cannot find agreed-upon definitions to start with. But Zhuangzi does seem to be trying to sympathize with everyone, or at least to leave no perspective out.