The main reason the idea that, "We should support disabled people, after all, anyone can become disabled at anytime!" does not work is because it makes rights for real disabled people contingent on it having hypothetical benefits to abled people. When the point of disability activism is to help disabled people, not appease the ableds.
Another reason is that eugenics is so baked into society that many people will readily admit they would rather die then be disabled. And people do not care much to help those they think should be dead.












