My comment is a tangent.
> The definition of disability is impairing one or more major life function.
A supplemental framing I've heard is that most of the obstacles that disabled people have to work around are obstacles that society can remove. If all of those obstacles were removed, then the disabled person would be enabled, because that person would be able to live, shop, work, and travel just as other "abled" people can. For example, in the case of people who need wheelchairs, removing the physical obstacles would include designing sidewalks with ramps, buildings with elevators, public buses with wheelchair lifts, and home staircases which can support wheelchair lifts. There are also social obstacles, such as social and employment stigma against people with wheelchairs. Some possible interventions might not be socially or economically realistic everywhere, but perfect doesn't have to be the enemy of better.
For deaf people, restoring hearing using gene therapy removes one obstacle.
Restoring hearing with digital devices (that the user can find support for if the manufacturer goes out of business) removes an obstacle. Another (partially collective) intervention would be adding closed captions (and possibly sign language interpreting) to as many videos as possible.
> So. If they have that culture, is it bad for them to celebrate that they can share in it with their children?
Perhaps "celebrate" is more like "be relieved" that the children will temporarily lack a distraction - spoken language from neighbors, should hearing restoration methods become widespread - from learning to communicate with the deaf parents. Well, that's too strong of an assumption for me to make: a better assumption would be that the deaf parents are relieved that their born-deaf children will be more likely to understand their parents' experiences. Consider immigrants whose biological children don't become fluent in their respective parents' first language. It's not as if immigrants would prevent their children from learning the predominant language of the city they settled down in. Likewise, I find it unlikely that a deaf parent would actively impede a non-deaf child from learning spoken language.