Is postmodernism a pseudo-philosophy?

Some claim postmodernist philosophical writing (e.g. Derrida, Foucault, Lyotard, and Lacan) to be pseudo-philosophy. Are they right?

Arguments for

 * Postmodernism was exposed by the Sokal hoax. . See also Sokal hoax.
 * This is far from conclusive, being a mere single incident, as suggestive it may be.
 * Postmodernism was exposed by Sokal and Bricmont book Fashionable Nonsense (published as Intellectual Impostures in the U.K.).
 * Since the content of the book is not available online, the online reader has no way of putting this argument under stress by reviewing the book.
 * It is so by the duck test: if something looks like incomprehensible likely-meaningless text after first, second and third reading, there is a good chance it is meaningless text. The quotations from postmodernists given by Dawkins are suggestive.
 * The problematic passages are not entirely void of semantics, and therefore, they are probably not entirely meanigless.
 * According to Britannica, postmodernism states the following: "Reality, knowledge, and value are constructed by discourses; hence they can vary with them. This means that the discourse of modern science, when considered apart from the evidential standards internal to it, has no greater purchase on the truth than do alternative perspectives, including (for example) astrology and witchcraft." More does not need to be said.
 * Britannica is an Anglophone encyclopedia and it is not certain it gets postmodernism right.

Arguments against

 * Postmodernism is not a single monolith and therefore, it is unlikely to be possible to show it to be pseudo-philosophy without analyzing its different strands one at a time.
 * One could respond to this by adding "largely" into the motion.
 * One could argue that for something to be pseudo, it needs to have at least an appearance of the thing, here philosophy. It is questionable that these author create at least an appearance of philosophy.
 * In so far as enough lay people and even professionals seem convinced they are dealing with philosophy, the requirement given by the prefix pseudo- seems to be met.