6th March is an annual day of awareness in the US about the use of the word 'retard(ed)' as an insult. Spread the Word to End the Word is an initiative of Special Olympics, addressing the larger issue of the intent of the speaker, and the hurt caused to a whole population, whether intended or not.
Here are some examples of recent media that look at why both the colloquial use of the word itself, and the vilification of a population are unacceptable:
John McGinley on the 'r' word, Everyday Dish, KDVR Fox 31, 1st March 2013
A Word Gone Wrong, Lawrence Downes, New York Times, 2nd March 2013
Stopping The R-word Is Not Enough: Culture - Not Just Language - Must Change, Meghan Morris, Huffington Post, 22nd February 2013
Quiz: Do you get why this word hurts so much? Love That Max, 6th March 2013