It looks like the previous responders have high functioning Autistic children. That's great! My stepdaughter is very low functioning. She will never live by herself. She will never enjoy the thrill of dating or falling in love or marriage. She will never go anywhere by herself - she will always need supervision. She might hold a job through the specialized school she attends, but it will be a highly supervised, low interest job. She is 20 years old and she has rarely offered any expressive language. She can respond to certain things, but mostly, we don't know what goes on in her mind.
That, my friends, is a tragedy. Not only for those who love her, but for HER! My husband cries at times knowing that he can't enjoy a closer relationship with her. Now, they have a wonderful relationship, and she loves coming to visit Daddy... she stays with us for 2 months in the summer, and holidays.
As far as using the term Retarded... yes, that term has been bastardized and the true meaning has been lost. It now refers, even clinically, to a different sort of challenge, like other posters have said, but it generally is not used. Certainly not for Autistic folks.
As far as the tragedy... there are so many levels of Autism, and of course, we love our children (or step children) without bounds, but it can still be tragic.