Where do you think retard will be ten years down the line?

Exactly where stupid, idiot, and crazy are, probably. But it's not there yet, that's my point.

And you do realize people only use the word stupid to describe when someone is being stupid.

Stupid never had a definition directly associated with mental handicaps like retarded did/does. Its first use in English (in the 1540s) already meant essentially what it means now (lacking ordinary mental quickness).

nobody is or has ever used the term to refer to those who are retarded as inferior or deserving-bad-treatment.

Actually, that's exactly what most people do. The use of the term as an insult implies that its former definition is inherently negative. If anything, your argument about the etymologies of stupid etc. would be better served as an argument for not using those words rather than using retarded.

Yes, it does consider people being retarded as people who do stupid things. However, isn't that the definition of being retarded?

Nope.

It's like the term "throw like a girl" being said to a guy. Or "you look like a man" being said to a girl.

Yup, and those are just as bad.

Nobody who uses the word retarded to describe or insult another does so because they dislike retarded people.

No, but in doing so they imply that the mentally handicapped are fundamentally inferior.

They use it because being called retarded is insulting for those who are not.

They use it because they think being called retarded is insulting, implying that they think being mentally handicapped is fundamentally a bad thing. See my previous point.

Using the word negro to insult a person is to say "if you were more like a black person you would be a worse person".

And using the word retarded to insult a person is to say "if you were more like a mentally handicapped person you would be a worse person." You're just making the same argument over and over again, but it won't make sense no mater how many times you repeat it.

If you were to call a black person a negro, I doubt many would really take offense.

Well, now we're discussing pure hypotheticals with absolutely no evidence, so that's pretty much useless. I've stated my position, and you yours. I'm going to sleep now.