In some ways I agree with you CluelessGit. It seems that, for some words, no matter what new word you use people are going to use it as an insult. Most words to disabled people originally were meant to be medical/non-offensive, but as people used them as insults, they became offensive. It seems like a loosing battle. It also seems unfair to presume people mean to be offensive when they use the "wrong" word, I come from a small, >95% white town, where lots of people use words I consider offensive to refer to black people. But they don't mean to be offensive, it's just they don't know that it's not the "right" word to use, they don't know what word they should use. That doesn't mean it isn't offensive, but it means that they're not racist just for using a racist word. Intent is important.
On the other hand though, I think people have a right to be called words that they prefer and do not find insulting. Obviously you're not always in a position to ask, but if somebody says "I find that offensive, please don't call me that" I think that's their prerogative. If the general consensus is that a word is offensive to a group of people, I don't want to use it. I don't want to insult people, and if I can word things differently to avoid doing so, I will do, because I care about how I make people feel. You don't need to use words like "the R word", you can say "idiot" or a similar word which has the same sentiment but none of the offensive connotations.
Furthermore, some words are steeped in oppressive, discriminatory history - lots of offensive words are offensive to people because they are associated with discrimination, insults and personal attacks. I think these words in particular should be avoided, because they can often bring up painful memories for people, and you just can't shed that history and associations that come with that word. If you use those words, you're choosing to use words that you know are offensive and painful for people to hear, you know how they might be interpreted - so no mater what you said, your intent is at best thoughtless and at worst offensive and unkind. (I am using "you" in the general sense here, I do not mean that "metard" is one of those words, or that anybody here uses them!).