Collapse denial is one of the more frustrating parts of contemporary historiography. It feels rooted in contemporary post-modernism in academia: if we acknowledge the possibility of "collapse", then we create a rank order of civilization, in which the pre-collapse society is "better" than post-collapse society. Since, under modern postmodern doctrine, all societies are equally worthy, "collapse" therefore doesn't happen.

It's this mental impulses that drives us to utter drivel like "Rome never fell".

I strongly suggest Greg Ward-Perkins' books on the subject.