I was devastated when I first read it because I was expecting it to be like Red Mars for a colony generation-ship, but after I had some distance my impression is that it is super optimistic about how Earth is.

It's a relief to think that even if we do fuck up Earth in ways which seem like they may be very likely to happen, it is still such a good place for humans to live, ie better than any other planet we know of, even with serious terraforming efforts.