I would be far more careful in tossing aside the concept of fairness. Fairness still applies to your cave people. Sexual assault was never fair; it's true tha

I would be far more careful in tossing aside the concept of fairness. Fairness still applies to your cave people. Sexual assault was never fair; it's true that you can't do something earlier people could, but that unfairness is more than weighed about by the fairness granted to Sally. In this case, fairness would probably look like devoting more resources to poor countries so they don't have to go through the same "destroying the environment" cultural growth phase. First world country growth was predicated on the access to energy afforded to us by selling out the environment. We are attempting to cut off that avenue for other cultures. It seems fair to accelerate them past the point of needing to destroy the environment, rather than telling them they just have to deal with being a backwater since they don't have a way to generate the energy needed to become a bleeding edge society. In more practical terms, and avoiding the concept of fairness, lesser developed countries aren't going to simply acquiesce and stop. They have no reason to. Cutting off their access to large amounts of energy is going to fling them back into the 1700-1800s. Have you seen The 1% on Netflix? It'll look like that. A small number of highly advanced countries with access to plentiful energy and all the technology that brings, and then a large number of countries that are dirt poor. I would be surprised if you could even manufacture modern medicine without access to large amounts of power. It will create a global power struggle, and first world nations are going to have to police basically the entire world to ensure there aren't any revolts or nations that are refusing to willingly go back in time.