My assumption here is that the book, written for a broadly left-wing audience, was basically aiming to reassure the reader that the author was on their side and then move on as quickly as possible. The current contemporary progressive view on the subject—that conception/contraception/abortion is entirely a personal choice, and that it is inappropriate to apply any moral pressure to women about them—is one that assigns essentially zero value to future lives. So expanding further on the subject could only raise the question that, even if you don’t think abortion should be literally illegal, that people should have to explicitly take into account the welfare of the child (and other future people) into account when deciding. The longtermist’s support for abortion is inherently going to be a contingent, fact-specific one - and as that would not be a comforting thought for the target audience, the book instead moves on swiftly.
My assumption here is that the book, written for a broadly left-wing audience, was basically aiming to reassure the reader that the author was on their side and then move on as quickly as possible. The current contemporary progressive view on the subject—that conception/contraception/abortion is entirely a personal choice, and that it is inappropriate to apply any moral pressure to women about them—is one that assigns essentially zero value to future lives. So expanding further on the subject could only raise the question that, even if you don’t think abortion should be literally illegal, that people should have to explicitly take into account the welfare of the child (and other future people) into account when deciding. The longtermist’s support for abortion is inherently going to be a contingent, fact-specific one - and as that would not be a comforting thought for the target audience, the book instead moves on swiftly.