Again, Grendel, I think you hit the nail on the head.
If I gave my child, born without legs, prosthetic legs, would I be "fixing" his legs? No. I would be providing him the opportunity to walk. I am also sure that I would provide a wheelchair as well, because, I'm sure there are times that he wouldn't want to do the work of walking using the legs. Is it the same as being born able-bodied? No. Is it "fixing" them? No.
A CI is the same sort of thing. It is providing access in a way there was no access before. It doesn't change that they are deaf.