Well said Dion.
Whenver this debate comes up I'm always surprised to see how many people take it upon themselves to protect the language and remain true to the etymology of words. Such saviours of language! How would we ever survive without? Surely we'd slide down the slippery slope and, well, never be able to ever communicate with each other ever again!
The historical origin of the word '######' and its multiple meanings aren't being disputed here. The point is that the word '######' is often a term to denigrate and insult people (either challenged or not). It does so by labelling someone else as deficient and inferior and only has any meaning because it implies an analogy between the target of the word and the mentally challenged individuals generally. No one is saying the word should be banned from language or that it couldn't be appropriately used in other contexts. Rather that it should not be deployed as an insult against other people. Is that really so unreasonable or even difficult to understand?
As for the ad.... not a fan. I like the cause, obviously, but the ad misses the mark. In my opinion, people don't respond to those kinds of 'shock tactics'. And I don't get the point of the picture.