Some of you don't seem to understand about the Deaf. There is an unique culture that has been created by people who are profoundly deaf and choose to identify with others who are similarly deaf. In their minds, there is NOTHING wrong with them at all... us hearing people are the ones with the disability. Worse, in some instances, they go so far as to shun people who are hard of hearing because they're not truly Deaf, or they use hearing aids.
No, the Deaf are not in treatment, they are not considered psychotic, and yes, they, by and large, would prefer to give birth to deaf children rather than hearing.
If hearing impairments were treatable or able to be eradicated, an unique culture would disappear, and the Deaf are militantly opposed to that happening.
As far as terms go, deaf is generally a blanket for someone who cannot hear at all; Deaf is for people who have serious hearing loss/deafness and are part of Deaf Culture; hard of hearing is basically everyone who has hearing loss, doesn't identify with Deaf Culture, and whose hearing loss isn't caused by age. Hearing impaired are old farts who lost their hearing due to age, military service, blasting music from Victrolas, etc., and don't give a damn about being PC.
But you really must understand, Deaf Culture is unique and viable, and the Deaf will defend it until their last breath.