The implication being that the only reason I could disagree with the idea that there is no human nature is that I have never encountered critical theory, structuralism, or postmodernism. Actually, one can acknowledge that we are all immersed in social structures that shape our thought in ways that we can't objectively understand, that communication is fraught with signs asserting cultural preconceptions, that there is a close connection between knowledge and power, etc., while repudiating the idea that external reality is illusory or unknowable, or that human behaviour is purely a function of context.

Human beings are animals, and thus the product of evolution. We are not blank slates, but highly specialised machines with innate tendencies and potentials. Almost anyone could, with minimal difficulty, list any number of phenomena universal to any human society: pain (and aversion thereto), communication, laughter, anger, etc. It is avowedly extremely difficult to separate ourselves from our inculcated norms when reasoning about human nature, but that does not refute its existence.

Of course, suggesting that human beings have no natural tendencies evolved for their survival ignores an overwhelming preponderance of evidence accumulated by biologists over the past century. But you know that, having clearly studied the field.