Although the Oankali save the human race from extinction, it does not justify their manipulation and subordination of the species afterwards. Now admittedly, if the Oankali had not come along, the human race would be dead, gone, no more people to stand around and be proud to represent what is “human”. However, to be brought back with little control over your major life choices, with often the only alternative being suicide, is not a great second option.

If we were not given the pretext that the Oankali saved the human race, there would be no doubt of their immorality (at least by our standards). For the majority of the story, the humans are held on “ships”, and not allowed to go back to Earth until they have proven themselves loyal. The Oankali maximize their slavery by making the human race entirely dependent upon Oankali for reproduction. The humans who do escape and form resistance colonies are filled with sterile, desperate humans. In Adulthood Rites there is finally a “compromise” which involves sending a pure human colony to Mars, but this does not give the humans a much more desirable situation. If we were told of a race that would capture all humans, sterilize them, mate with them, and as a compromise send the only colony of fertile humans to Mars, I don’t think their would be much argument over how justifiable that is. The fact that the enslavement prevented the death of the species does not change the fact that it is enslavement. As I pointed out in a recent comment, a good moral action does not justify a bad one.

I would even cast doubt on how “good” the action of saving the human race was in the first place. It seems to me that it was more of a coincidence of sorts that it was good moral action, for the Oankali were not rescuing humans because they felt it was the right thing to do, they captured humans for their own genetic purposes. If instead the human race was about to fly off to some other galaxy all at once, the Oankali could have very well done the same thing.

The Oankali’s actions cannot be justified morally, even if they are to be interpreted as advantageous to the human race. The basics for our morals lie in the right to make a choice. If I do something to you that others or I interpret as being ultimately beneficial without giving you a choice or asking your opinion, it is immoral. It might not always get an objection, such as when Lilith learns how her cancer was removed, but it always warrants one, such as the resistors.