Even if we do leave, it's unlikely that we do so for a very long time so taking care of the planet makes sense even if you intend to discard our crib. Similarly

Even if we do leave, it's unlikely that we do so for a very long time so taking care of the planet makes sense even if you intend to discard our crib. Similarly in the nearer term if we had a unified goal to colonize a near planet/moon that's still going to take a huge long term effort to do more than the equivalent of putting a tent up on an island off the coast to get that colony established (if it can ever be self-sufficient).