The unfortunate part about Aurora is that it is "optimistic" only in the context of all of the Red Mars trilogy, and 2312, and really only in the last chapter, where...
SPOILERS below
the characters go "well, eff it, I guess we have to make it work here on Earth". It seems to me that, in the arc of KSR's work, Aurora is the effective acceptance that humans will have to make Earth work for them, for better or worse, even as they collectively wrecked the planet. And that seems a nice segue into New York 2140.
Aurora is also told from the PoV of characters that are extremely anti-extrasolar travel.
SPOILERS below
Note however at the end of the book cryo-sleep is developed. This technology removes the main moral argument and technological difficulty against extra-solar travel as presented in the book. It is even noted in the book that a new wave of human colonization is taking place. KSR seems to be making both arguments at once but only telling one side of the story.
You do make an interesting point which I didn't emphasize: Aurora also makes a moral argument against generation ships.
But I think things get more complicated still. If you accept the book's argument, accept cryogenic sleep, but also accept that Earth is something like the biggest generation ship we have, then where do we stand? If we accept that cryogenic sleep solves that part of the moral argument, then we kind of walked into Woody Allen's plot for Sleeper (that is, why not sleep right here on Earth until things improve?) These are really tough questions to consider.
Needless to say, I think Aurora is the deepest, most introspective work that KSR has produced.
>And what you do then if you're not very lucky on arrival.
Option 1: Go to sleep and go home.
Option 2: Setup a small research station in a spun up asteroid and get terraforming.
Option 2 is much nicer with cryo-sleep. Try a terraforming experiment and sleep for 50 years to see how it worked out. You can even cycle people between Earth and the research station (see the plot of Alien). Planetary Geologists can live their lives on geologic time scales.
Or you could improve your odds by sending robots or small teams to many different stars (sleep, explore, sleep). You don't need to bring a full-cycle ecosystem until you decide to stay. Find good planetary sites and then send over the supplies.
My read of Aurora was that interstellar colonization was about to take place, but the PoV characters were against it.
SPOILERS below
the characters go "well, eff it, I guess we have to make it work here on Earth". It seems to me that, in the arc of KSR's work, Aurora is the effective acceptance that humans will have to make Earth work for them, for better or worse, even as they collectively wrecked the planet. And that seems a nice segue into New York 2140.