Does anybody seriously believe that reality itself is merely a function of language, thought and social convention? Some postmodernists like to say this ("reality is socially constructed"), but I doubt any of them would be willing to drink arsenic that has been socially reconstructed into harmless water. Furthermore, if reality is a function of these other factors, then one could not expect anything unexpected to happen (in a reality that is a function of thought, why should a volcano suddenly erupt if nobody thought of it?); yet the unexpected clearly does happen.
So why do people stick to extreme versions of anti-realism and constructivism, when more moderate positions that don't deny an external reality, yet still conserve the valuable aspects of postmodernism (understanding of culture, power structures, categorization and convention; deconstruction of beliefs & ideologies; interpretations of and assignment of meaning to natural phenomena; etc.), are perfectly reasonable and tenable?