Harper's analysis includes such factors (he pays a great deal of attention to global climate, particularly the characteristics of the Roman Climate Optimum, which spanned from 200 BCE to 150 CE, and other ecological, political, cultural, and technical factors.

It's also true that disease, as with many other pathologies, tends to observe Murphy's Law of Thermodynamics: things get worse under pressure.

Overexploitation of natural resources (soil depletion, deforestation, elimination of megafauna, depletion of watersheds and aquifers, exhaustion of mineral resources) all contribute to a general weakening of the civilisation which invokes these circumstances. It's worth noting that the Western Roman Empire at the time of its collapse was not generally in a state of pervasive famine.

And Harper isn't giving a One True Way response, he is carefully, with a great deal of historigraphic and scientific evidence building the case that, as I noted above, civilisations and pathogens co-evolve. (My expansion of that to networks or systems and pathologies generally is my own armchair contribution, though based on my own observations of numerous examples at first hand myself.)

As much as I appreciate and respect Socrates, he (as with virtually all pre-Baconian philosophers) relied strongly on reason and extremely unsystematic chosen exemplars to posit hypotheses, many of which have since proven greatly mistaken. (His student's student Aristotle polished this to a fine art.) Baconian science is empirical, Socrates is best known for an interrogative technique.

This isn't to say that some of the suggestions made by Socrates and other philosophers are necessarily wrong. But it is quite rare for same to have been grounded in anything remotely resembling what we'd now call scientific knowledge, a phrase whose apparent redundancy is best resolved by noting that "science" now means not merely knowledge but the systematic approach of observing, deducing, testing, and validating hypotheses, something Socrates did not practice, and Harper has.

Which isn't to say that the shallow interpretation of Harper's narrative might not also be false. But for a third time, that's not my point, the co-evolution of systems and pathologies is, and I'd hope that at least some of my readers here have managed to grasp that concept despite my own bungled attempts to express it.