As a hearing parent of a deaf child. I feel that if an adult wants one, and is considered a candidate, then by all means, do what ever they can to get one. As a parent, it is YOUR responsibility to do your research. Then, after considering all options, make your decision. It is a family matter. If the parents decide to implant the child, so be it. BUT, the family must be open to learning sign also. As said above, there will be times when communication is vital, and the CI will not be on the child.
One of the main objectives is to raise a child that is capable of effective communication. A parents responsibility to the child is to prepare teh child for life when they become an adult. A big part of that is equiping the child with whatever toolsare necessary for the child to be happy, successful, and adaptable through the stages in thier life. If the parent does not do this for the child, then shame on them. I am by no means saying that if a parent does not get the child a CI, that the child will not be happy, successful or well rounded. The CI is a tool, it is nto the right tool for all jobs and all people, but when used in most circumstances, and with training, it becomes an incredible assett.