Except that with "retard" and quite a few others, there are genuine traits that are undesirable to most people, thus the constant cycling of terms. Technical terms come in to general and pejorative use, then new technical terms come in to be less pejorative. This the terms more and more vaguely refer to the condition when referencing actual mentally handicapped people.
~~idiot~~ ~~moron~~ ~~cretin~~ ~~retard~~ (from '[profound] mental retardation')
All technical or health terms that have been cycled into being slurs in common use. Some more terms that have made their way into pejorative use:
~~Handicapped~~ (not so much pejoratively used, but being cycled out anyways) ~~Special~~ ~~Differently Abled~~
I'm sure any new technical terms that are used will be picked up for pejorative use soon enough. But "mentally retarded" was and is an apt description, it's just not socially acceptable anymore because of it's ease of use as an insult, and the concomitant public view and usage of the word.
Absofuckinglutely. This is what I do, and what she does, though our methods of exploration vary.