Well, part of the problem with "postmodernism" as an umbrella term is the absence of a single school or theory associated with it.
To me the defining work on the subject would be Fred Jameson's, which reflects even less positively on the phenomenon than Kel might.
Which goes to show that it's not really a useful term in mainstream political debate—it just becomes a sort of anti-intellectual bogey word that means "theory gobbledegook that I, a rational and serious person, do not want to engage with".
The real underlying debate is one between the premise of a holistic and all-encompassing political reason suitable to the implementation of a "rational" technocratic policy in every circumstance, and the premise that such a thing has not, does not and can not exist. I know I would rather remain on the side of those who are sceptical about the uses and limits of reason.Â