And to add a couple more layers. I know two young people right now with Down Syndrome. They are doing well. They may or may not be able to pursue their dreams (well, that's what dreams are for anyway), but they are certainly much like any other teenager.
One is a potential business owner. His mother and father purchased a shop, and the young guy is working at it right now. The parents are hoping that if the business succeeds he can take it on as an adult. Why did they do it? Because the parents correctly saw that a lot of adult service providers and professionals in general were too damn dismissive of their kids. So they said if the professionals won't get their act together, I will.
It's working and the shop has become an icon in the community for people with disabilities.
Another young lady is a social butterfly and doing well. Active in extracurricular activities, she has created a club at the school and has a wide social network. She also works at the shop of the other family's I discussed above. Her dreams may change (she likes to sing and dreams of stardom), but she's being given a steady life preparation from her parents as well as the school.
If you search around, you're going to find out that social expectations and professional opinion has shifted over the last 20 years. These kids haven't changed, the interventions and professional orientations have. They are going to college (even if it is modified programming), they are holding regular jobs, heck some of them are even business owners themselves.
And I myself am the sibling of a young adult with a form of autism. He's treasured by his manufacturing employer, has his own place, and pays for his rent. He is on benefits and does the careful dance to keep them, because he also has a light amount of assisted living from staff.
Folks, assessments and life prognosis at a young age is tricky stuff that can indeed become overly gloomy if it isn't spot on. When I was 5 I was diagnosed as being mentally retarded and my folks were told right then and there that my life, their hopes for me were dead. They were told many of the same things with my brother.
We came out differently in our outcomes, but I think the variance in outcomes with disabilities, in addition to the real joys, triumphs, and defeats in life make people with disabilities just as worthy of experiencing it as anyone else.