I disagree. There are lots of things mean people say that hurt just as much or worse. But then again anybody that is going to use the world to harm is just as capable and likely to use physical violence or other colorful language or worse. 

The problem isn't the word (or so many others) it is mean people and you cannot fix that by corrupting the language so many people rely on to communicate every beautiful frustrating element of mortality.

Retarded was the word experts with degrees used to label such individuals because it best fit the symptoms. Why let bad people take that away? Try stealing the word deaf from the deaf community and I bet they wouldn't let you.

Honestly how much power do you want to give bad people?

Why let them dictate terms to you and I and all of society? If you hate how they use the word make up for it by using it better, in a way that removes unnecessary stigma.