Okay, if I'm counting so far, Sicarius values shoes, fire, religion, philosophy, medicine, education, and mass communication abilities. Many are products of civilization, and some have achieved a pinnacle of relevance in human life after the advent of civilization. (Fur shoes, don't count to me, I don't think we should wear animals as a fashion statement, but whatever floats your boat).
But, what is civilization? A civilization is a society or culture group normally defined as a complex society characterized by the practice of agriculture and settlement in cities. Compared with other cultures, members of a civilization are organized into a diverse division of labor and an intricate social hierarchy.
Sicarius, I assume you take except with agriculture and city-living? Is it farming only or also the domestication of animals you reject? Will your world not contain cows, pigs, goats, dogs, cats, etc.?
Regardless, it is naïve to argue that agriculture and city-living themselves are unsustainable - after all cities have been around for thousands of years - I call that a proven track-record. What you call unsustainable is an issue of carrying capacity – that we will eventually exceed the ability to provide for an expansion of city-living by current modes of agricultural production. Well, as others have pointed out, that has happened many, many times before pre-agriculture and post-agriculture. So, I don't see the value of your sustainability argument - every social ordering is sustainable/unsustainable depending on resource over-consumption.
Here’s the $64,000 question, where do you draw the line? In your brave new world there will be medicine, shoes, clothes, fire, education, religion, and philosophy to a degree. Yet, there will be no cities, cars, Tivos, McDonald’s, or television. What else are you going to throw out the window? What will people do to support their new hunter-gatherer lifestyle? If farming and ranching are out, will you teach us how to hunt again and will there be enough game? If farming is in, what techniques do you reject? Is the Amish way of life sustainable in your version of sustainability?