The first phase begins with "cutting out" humans regarded as "others", e.g. by labeling them pejoratively as "retards", "cripples", etc. and ends with institutionalization, sterilization, or even euthanasia, including "mercy killings".
The second phase is often called the "medical model" in which humans become their disease/condition and undergo rehabilitation. It is assumed that those "suffering" some condition wish to "find (or at least seek) a cure."
The third phase, the "social model" is being grudgingly entered because we still consider "difference" to be "inferiority" as in the first phase. This phase often includes Centers for Independent Living or Living Skills Training programs.
In the "diversity model" human rights are considered the basis, rather than "disability" because the latter inserts the arbitrary "ability-disability" attitude.
In summary, the founding point of view is in Peter Singer's "It does not seem quite wise to increase any further draining of limited resources by increasing the number of children with impairments” which is echoed throughout Bioethical literature long after Bucky Fuller's proof that we live in a world not of "limited resources", i.e. scarcity, but in a time of huge surpluses in the Commons of plenty.
Saving one life does not demand/imply the necessity for taking away a life. In fact by enabling inclusion our wealth is increased. Biodiversity is essential to human progress/innovation. It is the fundamental building block of evolution. Every species that became extinct failed because of over-specialization and the shortage of diversity that would give the environment something to select from.
Because bioethicists are reluctant/unable to understand that we are all in this together, they are a major part of the problem rather than any sort of solution - in fact functional diversity as a requirement for civilization is apparent whenever we learn simplicity from the "simple minded" who are mainly warehoused without the opportunity to contribute their diversity of understanding to "educated fools."