Yeah, ethics of generation ships is interesting. But I'd say the problem is present in attenuated form even today. Is it ethical to give birth to beings (our children) who haven't asked to be born? Indeed the negative answer to this question is the basis of several anti-natalist philosophies: https://en.wikipedia.org/wiki/Antinatalism

> some of the settlers did stay behind to work with the materials of the system's asteroid belt to make space habitats.

The author was clearly unsympathetic to them. They died rather quickly and all they got in the book was a short "signals stopped coming" mention (which was another infuriating thing).