Paul Kjellberg, in his contribution ("Sextus Empiricus, Zhuangzi, and Xunzi on 'Why Be Skeptical?'") to Essays on Skepticism, Relativism, and Ethics in the Zhuangzi, quotes Xunzi's (c. 312-? B.C.E.) negative assessment of Zhuangzi's philosophy: "Zhuangzi was obsessed by nature and did not know the human", and attempts to determine what it is exactly that forms the basis of this criticism. He offers three possible interpretations of Zhuangzi which might have led to this assessment and settles on his ostensible belief that one who spontaneously follows his own natural inclinations will 'do the right thing'. Xunzi, we must remember, is famous for having said, "human nature is bad", in contrast to his fellow interpreter of Confucius, Mencius, who declared human nature essentially good, though deeply injured. Thus, Xunzi fears that if the world was to follow Zhuangzi's exhortations to live 'naturally', as opposed to following a strict regime of self-cultivation of culturally realized ethics, it would quickly go amuck.
I would like to offer a few ideas in response. The first is that Kjellberg, though he admits the possibility that he did not, largely assumes that Xunzi understood the philosophy of Zz. It seems much more likely to me that he probably did not. I would suggest that very few ever have, quite possibly because it is not coherent enough to understand. (Not because it is 'too deep' to understand.) And this is somewhat by design. Zz was more interested in providing an occasion for his audience to discover their own experience of reality rather than his.
But quite apart from this general philosophical ambiguity, Xunzi came to Zz with an agenda which in effect disallowed understanding him. Quite simply, he was biased and found (created) the negatives he wanted in the thought of an opposing school. Moreover, I believe that the only way to have any understanding of Zz at all it is necessary to experience that of which he spoke. His philosophy is not a series of propositions which we can assess on the basis of logic, but something whose only proof is in the living. Never did Zz endeavor to tell us how reality ' is'.
And this segues into what I think is a generally mistaken approach to understanding Zhuangzi's advocacy of spontaneous, 'natural', living, namely the assumption that it is somehow universally applicable. People protest, like Xunzi, that if everyone 'goes with the flow' evil will run rampant; pedophiles will have their ethical justification. Yet never did Zhuangzi proclaim 'going with the flow' as a path for everyone to follow; indeed, to do so would be to simply add one more prescribing voice to the cacophony of ethical imperatives.
What Zhuangzi actually advocates is experiencing one's being-in-the-world in such a transformative way that 'going with the flow' happens. In other words, this can only happen in the sage. We might say, it is the privilege of the sage, for only in the sage does it happen. Zhuangzi does not present a philosophy applicable to the world at large, but rather suggests a path which those inclined might consider should they wish. Though he may question the efficacy in terms of allowing freedom and ease of Xunzi's approach, he does not see any approach as contending for a universally applicable understanding of Reality.
You can check out Scott's writings on Zhuangzi here.