In the 70s there was an "appropriate tech" movement. Nobody was suggesting everybody had to go back to the caves and live in squalor to have a sustainable economy.
But what we have now is certainly NOT sustainable, and it's going to involve a certain amount of degrowth and ratcheting down energy use to make it sustainable - and the people in the wealthy western nations are the ones who are going to have to ratchet down the most.
ixi