So the deaths of millions during the Justinian (and other) plagues, the numerous wars and barbarian invasions, the plunging of Europe into a tribal, brutal Dark Age, and the near-complete eradication of Roman technology and culture was "doing rather well"?
You read history in a very different way to me.
Indeed. Few modern historians now consider the 'Dark Ages' to be a time of cultural and economic deterioration - that term was invented during the Renaissance to stress the advances being made in their 'modern' era. And plagues hardly started because of the Roman collapse - Hans Zinsser's 'Rats, Lice and History' gives an enthralling record of humanity's battle with plague, smallpox and typhoid going back to pre-classical times...
For Simon's hypothesis to be true, the broad sweep of history has to show advance. Of course there will be local reverses - our two recent World Wars are an example. But broadly, life in 1000 was better than life in 500, life in 1500 better still, and so on. Why we like to think (totally erroneously) that civilisation is on an environmental knife-edge beats me. You would have thought that the constant failed predictions of disaster throughout the ages would have ceased by now. But so long as environmentalists have grants, the dire warnings seem to keep coming...
Incidentally, I suspect we have wandered far from the original topic. But for the life of me, I can't remember what it was....