If I understand this outline correctly, we end up with multiple sustainable cultures, each adapted to its local environment. I do believe that multiple cultures will be necessary in a future human “ecosystem” providing mutual checks a balances similarly to how multiple species interact in climax ecosystems.
I have done some simple thought experiments.
I put two cultures in adjacent identical regions. The U culture does not control its population and/or consumes resources at a rate exceeding the renewal rate. The S culture controls its population and never consumes resources at a rate exceeding the renewal rate. Almost always the U culture eliminates the S culture (in the conflict, a larger population and/or greater resource use is decisive).
I put seven different S-type cultures in seven equal regions with each region neighboring at least three other regions. All cultures communicate freely with adjacent cultures without changing their own culture. Each culture nevertheless evolves in its own way. One of the cultures develops U-type characteristics. Usually, the remaining six are able to jointly react to constrain and modify (“heal” back to S-type) or destroy the U-type culture (in the potential or actual conflict, the combined populations and resources of the six S-type cultures suffice). The region of a destroyed culture is repopulated with volunteers from each of the remaining six cultures with a new “hybrid” culture containing roughly equal elements from each of the “parent” cultures.
The importance of many different cultures of “equal” size is that if one culture is significantly larger than the others, then the difficulty of dealing with it in the event that it mutates to a U-type culture becomes too great for the neighbors to cope with.