This is an interesting take and it got me thinking. The replacement rate in the US is
not 4. In fact, I would imagine that 4 is probably unsustainable. I like to see money more as a chemical gradient a la chemotaxis, though more clever people than I call it a carrot. With inflation the carrot is being removed, perhaps even being used as a stick. A superfluity of resources without controls of some sort may well lead to runaway growth, and I presume with the relative expenses of everything that there is an unsustainable imbalance at the fundamental level excess demand for intrinsically limited supply.
Of course the inflation model is applicable outside of the purely monetary. The more people you have the larger the labor army, and with each number added to that the less valuable the individual becomes even in terms of highly specialized labor, because ostensibly this can essentially be predicted with a distribution and with the way people are commoditized in most positions and companies these day, excellence is neither expected, sought for, nor wanted. This is still within the realms of the economists wheelhouse.
I would argue there's a third inflation, social inflation, as well. And this essentially hinges on the same principal that the labor army does: more people, less individual value (“a single death is a tragedy, a million deaths are a statistic”). And I would posit that the decrements have been seriously exacerbated in this realm by social media, television, celebrity, and so forth. I would also point out that the civil rights movement and women's lib has also (rightly) had a profound effect on social orientation that has yet to fully manifest itself.
If I recall correctly many developed nations have declining "native" populations. I'm unsure of the causal factors, but I wouldn't be surprised if it was in some ways an instinctual aversion to these sorts scaling laws. If I'm not mistaken Dunbar's number is roughly adhered to in nature, so it makes sense that there is somewhat of a drive to limit pack/civilizations size.