This is unfortunate misunderstanding. It's the deconstructive postmodernism that did the discreditation of Stage 4. Author in the paragraphs after "Deconstructive postmodernism" explains that first postmodernists were okay because they understood stage 4 rationality and they actually made forays toward stage 5. But their most vocal followers did not understood stage 4 at all and so they bastardized it.