I may have phrased it poorly, but what I meant by ‘postmodernism’ was thinkers like Foucault, and those heavily influenced by him. For example, think Butler and her idea that gender is ‘performative’, which is rubbish because gender is clearly 100% biological.

(Stating that gender is 100% biological is not anti-LGBT. Even in LGBT individuals, it is their neurology that makes them LGBT, not performativity or social construction. It was even part of the basic argument for LGBT rights, at least 10 years ago, remember Born This Way by Lady Gaga?)