Adorno, Horkheimer, Benjamin, Marcuse, Habermas etc. are definitely not "postmodern." (Said, on the other hand, often is considered po-mo.) Even if they were, you shouldn't simply dismiss them as "garbage."
What I find interesting is just how prescient a lot of the postmodern theorists were...
Roland Barthes' death of the author? Seems spot on to me! Twitter and Facebook have ended the hegemony of the narrative and replaced it with a billion people all shouting at once. We end up with emergent and algorithmic storytelling that is truly not created by any single author.
Jean Baudrillard's Hyper reality? Memes are a great example. The original context is so far gone that all we're left with is an endless procession of signs and signifiers and the next page on /r/AnimalAdvice.
Marshall McLuhan's medium is the message? Artists of all kinds suffer as their creations are digitized and removed from the economy while the entities that own the digital faucets at Google and Apple make record profits.
None of these guys are very easy to read, I'll admit that, but there are some amazing insights especially when you consider they were writing this stuff 30-50 years ago.
A lot of non-European people complain that they are indiciferable or garbage just because they are not accustomed to their language and cultural references, which is not totally unlike Blub programmer complaining about the difficult LISP or Haskell concepts.
That and the anglo-saxon mentality on philosophy is radically different (not necessarily better, as its proponents claim).
(As for stuff like the Sokal affair, nobody batted an eye or called CS, physics, biology etc "bullshit" when when tons of Markov-chain generated "papers" were published in hard science peer-reviewed journals -- here's one such incident for reference: http://www.nature.com/news/publishers-withdraw-more-than-120... ).
