Sure, not every sort of disease or pestilence should be interpreted as a clear chastisement from God, at least beyond the sense that disease in general is a consequence of our fallen human hature. There has always been disease in human experience, and there always will be. But it was only natural for the people dealing with the Black death to assume that there was, in fact, just that sort of chastisement at hand. The totally unprecedented scale of it alone was a clear "sign" to them. Is God constrained by any "law" to only chastise His wayward children via clearly "supernatural" means, or does His sovereignty extent to employing apparently natural occurences, too, especially when they clearly appear to be on a scale beyond that which has "natural" precedent?
Regarding your objection that epidemic-scale diseases cannot be attributed to any sort of chastisement, unless one is willing to concede that God favors the wealthy in their course: I can only deny that such was the case during the Black Death. As far as I can tell, there was no particular advantage to being wealthy at all. All social classes died like flies in this epidemic. The wealthy tended to live in towns, and the higher population density of towns, of course, was one of the key ingredients in the spread of the plague. Also, the state of medical knowledge and procedures in the 14th Century was utterly insufficient to deal with the Black Plague, and no amount of money could procure medical "solutions" for the wealthy. If anything, the extremely poor rural peasant class had the best chance of survival, as their contact with others was, by the very fact of their lack of neighbors, much more limited than that of village- and city-dwellers.
Before we go any further, let me ask the rhetorical question: Are the people of the world, right now, the most wicked and sinful people in the entire history of the world?
I say this as a rhetorical question, because right now, we face a plague so fearsome as to make the combined black plagues of the 14th and 17th centuries combined look like puny in comparison.
Some estimates put the potential mortality of the Avian flu at well over a billion people. Even the most recalcitrant and isolated governments of the world, such as North Korea, have been persuaded by their medical doctors to fully participate with any means the world can come up with to try and mitigate this horror.
If one million people a day died from this disease, it would still be almost three years to kill a billion people. And it may kill one billion people in just six months.
The United States will likely do well, compared to many other nations. Perhaps only one out of every 10 people you personally know will die. On average. Entire families you know might be wiped out. Every person in a small town. Most of the people in an apartment building. Others will likely survived unscathed, except psychologically.
In the 1980s, I interviewed some of the survivors of the Spanish flu epidemic. It only killed about 3% of the world’s population at the time, and 1/3rd of the world’s population was infected. It only had a mortality rate of 10-20%.
The mortality rate of those infected with Avian flu has remained at around 60%. If 1/3rd of the world was infected with Avian flu, at that mortality rate, 1.2 billion people would die. 1,200,000,000.
30,000,000 American sinners? If we are lucky.