Comment by keyringlight

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).