I agree it's insane to talk about terraforming other planets to make them livable when we have a pre-terraformed planet. It will be less work to fix our problems than try to create a whole new biosphere. We don't understand all the processes that take place in 1 cubic foot of forest soil. We will never replicate Earth on a currently barren planet.
So to that end, restoring forests and grasslands may be our best hope to bring down atmospheric carbon to comfortable levels.