Since I am deaf, I have more than a passing interest in this issue- and more than a few opinions on the matter. As a member of the Deaf community, I have some reservations regarding the ethics of CI but since that is not the focus of this discussion I will try to withhold those sentiments.
The pros and cons of CI will in my opinion vary with the individual who is receiving the CI. For a person who has an acquired loss (late-deafened), a CI may be the perfect answer. For a child with a congenital loss, a CI may be helpful, but in my opinion is not a perfect solution all in itself.
As to who would want one, again that is a matter of choice and will depend upon the individual. And here is where the ethical considerations come in that I really don't want to address because they are to me a large part of the issue. Suffice to say that an adult who suffers an acquired hearing loss will likely want to pursue a CI if they can afford it because it will come the closest to returning them to a 'normal' state.