Yeah what the hell are you bringing down sydrome into this for? thats rediculous.
Well, the word 'retarded' is not used in polite conversation here. Using that word would be on par with the many racial slurs that no one would dare not use because we know better, and we know that one's race does not affect ones intelligence.
Say that word around someone with family that get hurt by the word and you will get a strong reaction. It's like saying, "man you are so dumb, it's like you are as dumb as someone with a genetic condition that lets them be taken advantage of and ridiculed by society".
Something comparable would be to say, " you are as dumb as a (blank)" - fill in the racial slur of your choice. Not very nice way to describe another human being either way. Neither person can help being who they are nor should they want or need to. Using the word 'retarded' as an insult is hugely painful to those born with many different kinds of medical problems.
You think someone with Down's syndrome can't possibly be on and read Arboristsite? THINK AGAIN.