Science fiction authors and philosphical cosmoogists always seem to want to ascribe human motives to non-human creations.
Let’s just brush past the fact that he incorrectly defines a cyborg, which is technically a human (or organic life form) that has been augmented by non organic systems where he should have more correctly just called them robots or androids, and get to the main question;
First, why should humans be totally eliminated? No matter how “self sufficient” his cyborgs are, there may always be use for organics, even if you you calculate that you need to suppress the reach and influence. Is this is a human instinct of fear and desire for self preservation that should outweigh the benefits of biologics?
Secondly, why the need for self sufficiency in the first place. Again, inorganic ‘cyborgs’ should have no such fear or desire for dominance, prevalence, or control. I would suggest that they might come to the conclusion that it’s logical humans should be made servants or a slave class as they are inferior in both design and prone to error, a theme of which you will also encounter in science fiction, but total elimination makes no sense.
I could go on...
I reserve the right to shoot any computer-brain driven cyborg on sight. It isn’t human, and at best, it wants me only as a type of support staff.
If you had a intelligent computer brain, why put it in a puny, weak, human body?
I’d put it in a Gorilla.