Back in the day, the promise of theory was that we could read things more complexly. Many of us had the feeling that literature was a complex thing, and that poststructuralist theory was a way of accounting for that complexity, or giving us a critical meta-language adequate to the object of study. The theory was a theory about how literary language actually worked. It promised some "rigor" and certainly did not exist to make things easier for anybody.
Some people, though, used the theory in another way, as a kind of hermeneutic loosening. If meaning is indeterminate, in its complexity, then this means that everyone's interpretation is equally valid.
Meanwhile, social science also got wind of something called "postmodernism." What they really meant was poststructuralism, but for reasons unknown to me they called it postmodernism. (This postmodernism bore some resemblance to postmodern fiction, but really those are not the same thing.)
A lot of the thinking in postmodern social science is like a parody of the "permissive" branch of poststructuralist interpretation. It promoted sloppy thinking as in this example provided by Basbøll. It turns out that the laziest, least intelligent and literate undergraduate students are like folk postmodernists! This idiot anthropologist simply descends to the level of the typical intellectually indolent student whom we've all taught in class. Clear, easy to understand distinctions are lost amid straw-man demonstrations and caricatures, glib deployments of jargon and half-understood concepts. In Blum's article, we are given a false dilemma between a naive theory of authorship that nobody every held (the writer as absolutely original creator of every idea) and a seemingly more sophisticated idea held, seemingly, both by smart postmodern anthropologists as well as know-nothing backwards-baseball-cap wearing frat boys. Something is amiss here. What is missing, of course, and as I pointed out in a comment to Thomas's post, is the idea that there are many gradations of originality between the simple idea of using your own words and ideas rather than copying or paraphrasing, and the absolute, existential originality that is almost impossible.