I haven't read the book, but I think a major problem around the IDW-style discussion of 'postmodernism' is that the term is somewhat overused, sometimes incorporting other forms of critical theory. Critical theory is the 'umbrella term' for theories that focus on power and oppression dynamics, and postmodern critical theory is only a subset of that, but this seems to be lost.

The problem is, if we want to return to a more rational discussion, the whole concept of critical theory itself has to be opposed, not just the postmodern variety. Marcuse is probably an even more problematic influence on the New Left than Foucault, even though Marcuse wasn't 'postmodern'!