The planet has finite resources, except for solar energy (and the occasional meteorite adding a few kilos of material). Limiting our resource use has limits, specifically, the limits of human population itself.
If we aren't willing to limit the human population, then our focus should be extraterrestrial colonization. There is no "fixing" the earth--you can't get around the fundamental resource scarcity. We're already running up against shortages of rare materials.
Interestingly, Star Trek's post-scarcity space utopia was based around (1) nearly infinite energy sources and (2) technology that converts energy into useful matter: food replicators, transporters, holodeck constructs, etc. If you think those two breakthroughs are feasible, then sure, you can stay on Earth and repair things. Otherwise, get out into the stars and find other resources to consume, both energy and materials.
(And if you think the energy problem is trivial, read Asimov's
The Last Question. Or read the manga adaptation
here or
here.
Given a long enough timeframe, entropy dictates humans choose between extinction or evacuation.)