On the other I think there is a valid point in looking over how language is used and what implications it has.
But to try and over correct it with new words is like trying to add another layer of paper to make the boat not leak. Since instead of saying you are a retard, now you just say: person with mental challenges.
It has the same result when used as an insult, it stigmatizes people with "retardation" and it still insults the other person.