Click here to access the letter by Eric Schechter, a retired professor of mathematics, posted on The Greanville Post.
The ignoring of the man-made system of capitalism is common among those upper-middle class professionals who want to enjoy a well-paid career. They go to great lengths to avoid offending their bosses who are themselves employed by, and serve, the ruling class of capitalists. Even Schechter is this letter does not name the system (although he may have omitted the name to avoid shocking McKibben and to increase his chances of getting a response). It has a name--capitalism. Hence, upper-middle class writers often treat the economic system as an absolute fixture of reality much like nature or gravity.