Disabled people generally weren't looking for euphemisms for these conditions, though. I think that is why it was so easy for these softening, abled-people-created terms to be co-opted by comedians. At least in part. The insincerity was already kind of dripping off the words. The essay I talk about at the top of this piece goes into the history a bit -- but most of the euphemisms were invented in the 80s by the non-disabled parents of disabled kids, or by organizations run by non-disabled people. They were well intentioned, but kind of prioritized sounding polite over actually showing respect, which kind of dovetails with the point of this essay in a nice way.
That said, it is absolutely true that no matter what word we use for certain disabilities (especially cognitive ones), it becomes synonymous with an insult. "Idiot" "moron" "lunatic" were all clinical terms. Then of course r*tard became hateful. Now people use Autistic or cognitively delayed as an insult at times. That indicates pretty clearly the problem is not the word, its the world's attitude.