This theory has obvious intended moral lessons; I'd actually be very curious as to why you perceive it as morally-neutral. Is is that you see the primary lesson as so obvious ("pillaging isn't a sustainable economy") that it doesn't appear to be didactic? I wouldn't be surprised if the lessons were the whole point of the theory; I've heard it used before as an analogy to criticize the Soviet Union's political structure and the United States' economic structure (by two different people, naturally).

Now that I think about it, since entire schools of morality can be roughly summarized as "morals are the codes of conduct that make your civilization work well", I doubt it's even possible to come up with a theory explaining a civilization's collapse without that theory inherently expressing a moral lesson. Even "external factors destroyed it" could be interpreted as "you should be more paranoid than they were about dangerous external factors".

Re: Why is the roman empire like a forest fire?

I expect that's an honest answer. I read it and thought: wow: it is so weird to hear an honest-sounding answer in response to the question of "Why do you believe that?" - rather than a story that serves as a defense of the original belief.