The breakdown of cultural hierarchies known as "postmodernism" is often seen in a simplistic way. After all, just being open to the value of pop culture does nothing to break down the difference. Only someone steeped already in high culture can even merge the two in a significant way, so the cheap anti-elitism is not really what it's all about. The standard way of thinking about it is as a kind of dignification of the popular, but then that implies it needs dignity it doesn't already have. It gains that dignity, presumably, by being in the company of something more dignified. Hence the hierarchy remains intact. Even to have a shock value of Mickey Mouse meets Dante you have to have a sense that they belong to different worlds.
So the real story here might be something different from what we have been told. I think it might involve the missing category of the middle-brow. For someone like me, the existence of Billy Collins is more of an affront than the success of the latest pop sensation. Everyone more or less enjoys some forms of popular or mass culture, or at least has stopped caring that someone else enjoys it. A sixty-year old today was born in 1953 so you would have to be a generation older not to have grown up on rock.
The literature that's survived from the 1950s is not Auchincloss but Kerouac.
Cultural studies and postmodernism are two names for the breaking of hierarchy. Postmodernism is a label what the artists themselves do; cultural studies is the academic study of mass culture. I reject call "poststructuralism" "postmdernism." That is a social science terminology.