I don't think you can dismiss the sustainability of meat-substitutes just because we as a society continue to use coal or import plastic. A bean-based veggie burger has a much lower environmental footprint regardless of those things. The major difference is that choosing to buy a meat-substitute instead of the real thing is a decision that people can individually make, even if just for one meal a week, while most of us don't have the ability to choose to close down a coal plant.