Just left this comment at What Really Happens When You Use the R-Word | John C. McGinley: "Actually, "retard" and "retarded" are not always used as put-downs. They're only used as put-downs when they're used rhetorically as put-downs. If you do a little googling, you will find every other euphemism for people who are developmentally disabled being used as a put-down, including "developmentally disabled". Compassion is about compassion, not about the words we use. We can say the most insulting words with compassion and sound compassionate, and the nicest words with hatred and sound hateful."
On the list of things many people don't understand: the meaning of a word changes with its context. Black teens can call each other nigger and know there's only respect or affection behind it. Sneer at someone and say, "You and what army, sweetheart?" and you'll probably get hit.