Like a lot of social questions, attitudes toward disability remediation only start getting really nasty when they intersect with people's identities -- which is probably what writers are getting at much of the time when they talk about "disability culture", although I think that's a less than ideal choice of words since cultures intersect only imperfectly with self-image. Now, at this point I could link to "Keep Your Identity Small" and wash my hands of the problem. Certainly that's the advice I'd give to anyone in the unlikely position of making conscious choices about their future relationship with disability. But that's a dodge, and there's enough situations where it's inadequate that I think the question deserves a real answer.
I don't think breaking our response to the identity construction of disability down in medical terms ("they're sick; it's our job to cure them") is going to get us anywhere: the social architecture of medicine makes it poorly suited to navigating scenarios which the patient wouldn't consider dysfunctional. Let's consider our response in sociological terms instead: it has medical consequences when alternatives are or may become available, but people take on all sorts of identities with quality-of-life implications.
Looked at through that lens, choosing to accept a disability when remedial measures are available becomes largely equivalent to e.g. taking a vow of silence. Public choice issues make this trickier (enough so that I could probably devote a fairly long post to them), but if we leave those out it looks to be well within the scope of social variation: a little weird, sure, but not obviously destructive and perhaps handy on a society-wide level if problems come up where isomorphic coping skills would be useful.
But then there's the issue of taking steps to spread disability identification: patients opting out of gene therapies which could resolve the disability for their children, campaigning against curative technologies, and so forth. To a certain extent this can be considered self-defensive, and it's probably best to keep the distinction in mind. But insofar as it involves nonconsensual withholding of potential cures, it seems equivalent to (to borrow an Iain M. Banks phrase) aggressive hegemonization, and strikes me as rude. Identities do not have a right to exist independent of their carriers' preferences, and attempts to render those preferences irrelevant should probably be discouraged.
The analogies to augmentive transhumanism are all fairly straightforward.
With apologies to Ed Regis.
Modern science has caused humankind to develop better cures and patches for once-debilitating conditions; people often survive maladies which would have killed them not long ago. In the wake of this and of a recently changing attitude regarding how cognitively disabled people might see the world, a disability rights movement came into swing in the 1970s. Increasingly, the attitude of disabled people was that it wasn't inherently bad to be disabled; a disability could be an intrinsic part of a person's self-image. Some people in wheelchairs, for instance, want badly to be able to walk - but some do not, and the mainstream attitude has historically not validated those people's experiences. This is where disability culture intersects the transhumanist movement. If it is possible to identify so strongly with a physical disability as to not want any cure, how does that mesh with believing that it is desirable to improve one's mind and body? Is it possible to identify as a happily disabled transhumanist?
This does not intend to suggest that transhumanism is a movement of eugenic warriors; it's hard to imagine anyone suggesting that folks who don't sign up for the "Harmless and easy cure for senescence" shot be sterilized. However, despite the fact that hardly anyone would identify emself as an eugenicist (a fine thing to call yourself once-upon-a-time in America, until the Nazis rendered the term unpopular,) literally eugenic attitudes in society prevail, e.g. the prevalent belief that people with Huntington's disease or schizophrenia who reproduce are cruel for hazarding the inheritance of their condition.
One wonders what disability culture would look like if people who are today in wheelchairs had access to technology that could repair their legs and allow them to walk. I wonder if people with congenital disabilities which would today require a wheelchair would have a choice about being cured, or whether the cure would be implemented in infancy. In 2007, a girl named Ashley who has an unknown brain disorder and cannot communicate or move herself effectively was given a series of radical procedures - hysterectomy, mastectomy and high estrogen doses - intended to make her easier to take care of. Was the literally non-consensual hysterectomy an eugenicist procedure? An immoral one? Was it in the spirit of transhumanism? In a future where Down syndrome can be prevented with a prenatal vaccine, would such a vaccine be moral? How about vaccines for "low-functioning" autism? At that rate, surely it would be possible to vaccinate for Asperger syndrome, depression, and ADHD, conditions which many people dislike and/or dislike having. (As an aside, with all the medically-repudiated yet widespread fear about vaccines causing autism, one can only imagine the panic an autism vaccine would cause.)
I don't have answers to these questions. I have feelings and impressions, but those are not very useful. The issue cannot be solved unilaterally by saying that only those who enthusiastically consent to certain medical procedures should be given them, because many people are incapable of giving clear consent, as in the Ashley treatment. Nor can it be clearly solved by suggesting only prophylactic measures against disabling conditions, because certainly some parents would forego those measures. In a transhuman future, is the birth of a nonverbal autistic a preventable tragedy? Is it less of a tragedy if the child is a savant? Nor can one say that only conditions without an accompanying culture should be eradicated. Even if the definition of 'culture' were not elusive, HIV/AIDS has a definite culture about it, and few people would suggest that HIV should not be eradicated.
It is not useful to ignore the role of disabled people and disability culture in the transhumanist movement. I believe that the future has a lot to offer many people with disabilities, including those who do not want a 'cure.' Transhumanism can encompass interest in diverse AAC methods, and I believe it should. Simple keyboard technology has made it possible for many otherwise nonverbal people to communicate eloquently, as have DynaVox devices and various iPad apps. It would delight me to see widespread discussion about more powerful AAC devices, which could enable us to perceive and act on the desires of those who cannot now communicate.
Nor has technology reached its limits in helping those with physical disabilities; wheelchairs are generally clumsy and heavy, and expensive for people without insurance - nearly inaccessible to people who live without insurance in impoverished areas of the world (or of the United States.) People who, like Stephen Hawking, become paralyzed by motor neuron diseases, do not all possess Stephen Hawking's access to high-tech communications devices (for which prices begin at thousands of dollars.) And people with disabilities like epilepsy or cerebral palsy are still often abused for their "demonic possession" or inaccurately stereotyped as mentally disabled. The transhumanist movement tends to advocate augmentation sans cure as far as physical disabilities are concerned, but there are people with mixed feelings about transhumanism as it applies to disability.
Disability is a hot button topic surrounded by widely varying spectra of beliefs. It directly affects humankind and is not often discussed rationally because of the subjective experiences people have had with varying disabilities. (The mother of a nonverbal autistic says, "There should be a cure for autism; I want my son to say he loves me." A nonverbal autistic communicating by AAC says "There shouldn't be a cure for autism; I want people to learn how I communicate my affection." Their conflicting beliefs do not predict radically different anticipated experiences.) So a rational, clear dialogue about disability is vital - for disabled people, their friends and families, and the world at large - in order to integrate these identities and experiences into the future and present of humankind.