Late to this thread.
Theoretically, the work of Sassure sums up nicely why we have evolving insults. He said that words are simply 'signs' and 'signifiers'. In other words, we have a concept in our mind, and we have a label we give that concept. Together, they become a word.
So, picture an object with 2 wheels, pedals, a saddle and a handlebar. That object is given the label 'bycicle.' Now, when you use the word bycicle, the person hearing your utterance pictures an object with 2 wheels, pedals, a saddle and a handlebar.
The words themselves (as in the 'labels) are neutral - they carry no meaning. It is the understanding that people have, the image they conjour in their minds, that gives the 'word' meaning.
More practically, I will challenge any word which disparages people with Special Needs/Disabilities/Additional Needs. I will do it again, and again, and again.
I've been known to email MNHQ with the history of a certain word (e.g. cretin) and explain why it is offensive.
I don't care if some people will have to think a little bit harder and use a non pejorative term to describe a person or a situation. I don't care if some people feel that their right to free speech is being curtailed. If they weren't so insensitive in the first place, they wouldn't use the words.
Why should my DD, who already has enough disabilities, put up with children mimicking her in the playground - children who, in her naivety, she thinks are trying to be friends? Why should my DH have to go up to them and ask them not to say those words about her? She's 7 years old.
As a parent of a child with a disability, it's my job to protect my DD. I also feel, by extension, that I have a responsibility to any child/adult with a disability.