Detractors of Zizek have lately attempted to discredit his work on procedural grounds. The more serious accusations are related to plagiarism — including the famous case of the paraphrased white supremacist book review and now a more recent incident involving quotes in his book Violence. When the story broke, I offered a weak defense of the first incident, which seems to have been genuinely inadvertant. On further reflection, though, it seems to me that Zizek was using his friend’s material in the same way academics use material from their research assistants — and I doubt anyone checks over every detail of a research assistant’s work, because that would miss the point of having a research assistant. The second incident was literally just a copy-editing error, which could happen to anyone.
At this point, I anticipate some readers would say that, even granting these incidents were unfortunate accidents, Zizek’s frenetic over-production makes them more likely. And this brings us to another set of trumped-up complaints about his supposed “self-plagiarism.” Apparently he needs to write things fresh every single time he publishes, or else he’s doing something akin to the most serious ethical violation in academia. As I once ranted on Twitter, the concept of “self-plagiarism” is incoherent, given that he’s passing off his own ideas as, you know, his own ideas. There are reasons to object to the repetition, of course, but virtually every author who has written a large amount has “self-plagiarized” at some point — I will certainly confess to this horrible sin.
And now, the goal posts move yet again: the fact that Zizek repeats himself shows that he has nothing new to say. To that I’d say: okay, why don’t you try synthesizing Lacan and Hegel in pursuit of a unified theory of ideology, subjectivity, and ontology! Such a mammoth intellectual project will necessarily require intensive labor, working and reworking concepts and arguments. Sometimes similar examples are bound to come to mind in various contexts. Sometimes it will seem that a previously written passage can’t be significantly improved upon and can simply be reintegrated into a new whole. Everyone who’s met or talked to Zizek knows that he works obsessively, often skipping out of social engagements to get back to his room and write. His intellectual project is what is most important to him, and the amount that he is producing is realistic given his lack of teaching commitments and administrative work.
In essence, Zizek’s procedure here is no different in principle from that of Husserl, who wrote and rewrote voluminous drafts and was continually “introducing” the project of transcendental phenomenology. The one thing that has changed is that Zizek is publishing his drafts as he goes. Perhaps it would be better in some way if he would wait longer between publications, but you can’t blame a non-traditional academic for sticking with the method that gained him enough notoreity to elbow his way into the philosophical conversation despite his lack of a traditional position. You can’t blame him if publishers are willing to print the latest incremental updates to his project as he produces them, nor can you blame him if enough people are willing to buy the things to make it economically viable.
Nor, indeed, is it the case that he is simply repeating himself over and over. There is development and change over time, for those with the patience and investment to watch for it. If you don’t have the requisite patience or investment, you are under no obligation to keep reading his stuff, just as you’re under no obligation to paw through all of the Husserliana, or all of Lacan’s seminars, or all the iterations of Hegel’s lectures on philosophy of religion, or…. The fact that you’re tired of Zizek and don’t want to bother anymore isn’t proof of his intellectual bankruptcy — indeed, if you use your own understandable fatigue and wandering attention as grounds to discredit a major thinker and dissuade people from taking him seriously, then maybe someone is intellectually bankrupt, and it’s not Zizek.
An und für sich 
Self-plagiarism has nothing to do with writing “things fresh every single time” any more than conventional plagiarism forbids use of other people’s ideas and research. In both cases it’s an issue of proper referencing and aimed at maintaining good research practice. In any case, with Zizek it’s largely redundant because he works outside the bounds of institutional control. It would be a terrible practice for a younger scholar to imitate in an attempt to boost their research output, however. I also find self-plagiarism aesthetically preferable to reading material that cites a dozen or more previous articles by the author, invariably on a similar topic, in an attempt to boost citations.