Some may choose not to use their voices if they think they will be difficult to understand or have inappropriate pitch or volume. Speech development depends greatly on one's ability to hear him or herself talk. For the deaf person, the foundation for learning speech which hearing people take for granted is not there. The situation has nothing to do with intelligence. Deaf people can read lips.
Hearing aids are assistive devices which improve hearing for some individuals.
A hearing aid may enable a person to hear someone's voice, even though she or he may not be able to understand distinct words. Just because someone wears a hearing aid does not mean the person hears normally. Deaf people are not very bright or educated because they have not learned to talk or do not use proper English grammar. Deaf people lead totally different lives from other people. Deaf people are set apart by only one thing.