The incest doesn’t excuse the torture. My thoughts and feelings about the violence, gore, and torture take up around a hundred times as many words as my opinion about the final chapter’s incest scene.
I would be comfortable warning someone about the violence and so on when recommending the book, in order that they make their own decision. With certain friends, I would be able to discuss it in depth. That’s not something noteworthy to this novel alone; see also Ender’s Game and The Magicians and Westworld for having particularly violent moments that earn some sort of caveat, and deserve discussion of their value to the novel as a whole.
I do not in any way ‘excuse’ the violent scenes, however. This is a violent novel. These violent delights have violent ends. If that’s not in-scope for someone, no amount of making excuses will help someone derive value from it. This is not a noteworthy point to make about this novel in specific, at least generically, unless one is interested in discussing societal mores and the tensions of tolerance and desire for ultraviolent content versus Western sexual repression.
(I’m not presenting here any specific viewpoint or opinions on the matter of the violence in this work, as those views are fully decoupled from my objection to the incest.)
Separately, I find the final sex scene to be needlessly detailed. Yes, that’s exactly what you’d have to do in an Adam/Eve scenario. No, I don’t want to read a portrayal of incest. Yes, it flows logically from the story. No, I don’t want to read a portrayal of incest. Yes, the incest is only a single page compared to one half of the book’s ultraviolent dedication. No, I don’t want to read a portrayal of incest.
Whatever your position regarding the book’s use of violence, I urge you to take caution in considering it to be of equivalent moral priority to the book’s use of incest. Perhaps for some, they are of equal priority weighting; but that is no guarantee, in most societal contexts, that they can be evaluated using equivalent methodologies. No amount of refactoring and generalization will defuse the “this is unacceptable” outcome of the incest as presented, without regarding how much or how little violence is presented at all — because the explicit detail provided does not contribute to the story.
In general, I expect incest scenes of the type written in this book’s conclusion will continue eliciting such hostility for the foreseeable future, remaining wholly uncorrelated from societal shifts in acceptance or rejection of violence in fiction. That last chapter has been a problem through thirty years of cultural shifts. Here’s to another thirty years of warning people about it.
Notably, if this was erotica rather than hard sci-fi, and the incest scene was a component of titillation in a work dedicated to that outcome, then I would have just ao3-tagged it and skipped reading that bit and given people a simple cw and recommended the story. The segment in question is presented as matter of fact non-erotic consequence and conclusion of the story, and so does not earn from me the shrug-whatever-next tolerance and the much simpler warnings that I grant to erotic works in general. However, that presents the one exception I would make in recommending this story: if I’m recommending it to someone with familiarity with romance novels, gothic novels, ao3 tagging, or pornhub categories, then I would absolutely have a much easier time expressing my discontent with the novel:
“The last chapter has some unnecessarily explicit incest for half a page or so, which is in keeping with the lurid violence and sex tone set by the rest of the book, but I think the author’s dedication to the purity of their art critically weakens the potential impact of their work.”
And then, having concluded the incest warning, I would proceed to deciding if a violence and gore warning was appropriate for my audience. But that’s far too abbreviated for use at HN, so HN gets the long form — and HN is not what I would deem a ‘violence-averse’ community, relative to some others, making it uncertain whether I consider the violence of use to discuss here at all.
I hope this helps offer some clarity into how one might evaluate two equally upsetting things by completely different processes without sacrificing internal logical consistency.