I agree with Ben that calling work "obscurantism" is not ad hominem. Academic obscurantism seems to me at least a problem and possibly an important phenomenon which needs understanding.
Warning: I'm not a Deleuze expert; I'm at best an amateur epistemologiost.
I do understand, however, that obscurantism and difficulty of topic are two entirely different things that are easy to confuse. The intelligent writers on the list below generally spend time looking for ways of differentiating the two.
- Alan Sokal does it in part by identifying episodes where prominent academics were
writing obscure prose which contained glaring inaccuracies in descriptions of scientific phenomena,
signalling that they were willing to write about what they did not
understand - and thus there is something going on beyond "these are
difficult concepts for the lay person".
- Martha Nussbaum does it in part by
identifying Judith Butler's unwillingness to examine multiple
interpretations of material.
- Chip Morningstar does it in part by noting how
different the process of exploring postmodern literary criticism is
from exploring other difficult material.
These three are, in order, a physicist, a noted philosopher and a noted programmer.
For all three of them, and for others, separating obscurantism from difficulty is a primary concern. They are all trying to identify the point at which meaning, rather than simply becoming more difficult, actually disappears into over-abstraction.
Here's Robinson, for instance, citing a passage from a journal called Human Studies:
Now, the usual defense
here is that to people within the scholar’s subfield, these words do
mean something clear. But this is false. Try asking them. See if they
give you the same definitions, and if those definitions are ever
particularly clear, or always include yet more abstractions.
One obvious problem with Deleuze et al is that it's impossible to find people who make what they're saying understandable. If you want to understand, say, relativity, you can find a huge number of experts who make it understandable, even though it is a very difficult concept and though you will have to work at it pretty hard. Finding a writer who sets out Deleuze clearly seems, in stark contrast, pretty much impossible.
Note that Foucault is not really in this group at all. He's a fairly good writer who throws in incomprehensible passages from time to time. According to Searle, Foucault once accused Derrida of obscurantisme terroriste, explaining:
"He writes so obscurely you can't tell what he's saying. That's the
obscurantism part. And then when you criticize him, he can always say,
'You didn't understand me; you're an idiot.' That's the terrorism
If academic obscurantism really does conceal an absence of worthwhile ideas, then one mystery is the extent to which people are doing it consciously, aware that their ideas are thin and relatively unimportant, and the extent to which they genuinely believe they are making intellectual breakthroughs, possibly because they have some different idea about what important intellectual breakthroughs actually are. It seems possible that some of them have a very non-standard conception of what ideas actually are - a conception that privileges language over the ideas that should be beneath.
Nathan Robinson, Academic Language and the Problem of Meaninglessness https://www.currentaffairs.org/2017/07/academic-language-and-the-problem-of-meaninglessness
Filip Buekens and Maarten Boudry, "The Dark Side of the Loon. Explaining the Temptations of Obscurantism" https://core.ac.uk/download/pdf/55704402.pdf
George Orwell, Politics and the English Language http://www.orwell.ru/library/essays/politics/english/e_polit/
Chip Morningstar, How to Deconstruct Almost Anything https://www.info.ucl.ac.be/~pvr/decon.html
John Searle on Foucault and the Obscurantism in French Philosophy http://www.openculture.com/2013/07/jean_searle_on_foucault_and_the_obscurantism_in_french_philosophy.html
Martha Nussbaum, "the Professor of Parody" https://faculty.georgetown.edu/irvinem/theory/Nussbaum-Butler-Critique-NR-2-99.pdf
Alan Sokal, Beyond the Hoax https://www.amazon.com.au/Beyond-Hoax-Science-Philosophy-Culture/dp/0199561834