The only thing unsustainable is an indefinitely growing population, but fortunately it's projected to level off. If so it renders the arbitrary objections a moot point.
The rich aren't numerous enough in number for it to matter, but more importantly, the linked highlights global disparity. Everyone in the West has a higher carbon footprint than poor countries just by living here. The resources consumed by the rich aren't ridiculously greater than the middle class.
This is all a moot point in the face of stagnant population growth. It would be no less sustainable for the West to consume more by virtue that the demand isn't infinite and technological innovation increases efficiency all the time.
