No, even if the electricity were carbon-free there would still be an opportunity cost in wasting ever-increasing amounts of it doing bitcoin mining instead of,

No, even if the electricity were carbon-free there would still be an opportunity cost in wasting ever-increasing amounts of it doing bitcoin mining instead of, say, aluminium smelting, or powering electric trains, or any other useful thing. Also just for the record, minimizing driving is a good way to combat climate change.