The weapon of choice of bigots is to blame their targets for their own behaviour, as though they were forced to act in the way they do. Below is a prime example:
http://news.bbc.co.uk/1/hi/uk/6601473.stm
In this article, employers are implicitly blaming Disabled people for causing them difficulty in employing us by our simple insistence on being treated with dignity - as though by doing so, we are forcing them to speak another language. If you used an overtly racist, homophobic or sexist term to an employee or co-worker, you'd rightly be in trouble. But I and many others have had disablist epithets used in our presence and been told not to be so "politically correct" when we object. This is an obvious double standard - and it can often come from the mouths of those who themselves have been vicitmised for being who they are.
Now - here's my challenge to you. It's often been my displeasure to encounter disablist words like "retard" being bandied about on messageboards without any cognizance on behalf of the writer of the potential effect of the use of the word on readers who may be disabled in some way - especially if they are developmentally-disabled - and who always bleat about "free speech" when you call them to account. So, I'm asking you to think before you use such words lightly. And if you cannot honestly find a valid reason to use them - find an alternate way of expressing yourself.