"If some of those affected do not like it, and I know that, I would not use it"
I've never met anyone with leartning diffulties, or any relative of a person with learning disabilities who doesn't hate the term "retarded".
"Nigger" was also in its time a straightforward descriptive term without any insulting implications. "Yid" is just the Yiddish for Jew. But these words have been used too often as insults, and in a context where people have been treated as less than human - they are no longer usable. And the same goes for "retarded" - it has the same impact on people as "Nigger" or "Yid"does.
I'm writing this in England. Maybe in America it's different - words can have different meanings and implications in different places.
As Marion put it so succinctly: "Attitude is more important than terminology, but since you have to use terms you should try to use the most acceptable one to the people most directly affected."