I worked with mentally handicapped kids a lot as an educator when I was younger (albeit in a different country). This wonderful article captures perfectly how, in the right environment, children with Down Syndrome can blossom, but how hard it can be for them as adults once society & red tape & bureaucracy all come into play. (I also worked with children who had Down Syndrome and had not grown up in the right environment- think abusive/dead/incarcerated/etc. parents. That got very depressing very fast, and I'm not sure I could do it again).

I think this also highlights how the increasingly geographically fragmented familial unit is problematic: in a culture where several generations of the same family lives under the same roof, the situation wouldn't be as dire. However, in our culture it is typical to have only small portions of a family living together, and for children to move away and live on their own, potentially hundreds of miles away. No situation is perfect, of course - but it's still something to ponder (and it affects other social groups as well, for instance the elderly).

There was a wonderful American Life a while back on a similar topic, about a mother dealing with her adult son who had a mental disability (can't remember if it was autism or Down), and fearing for what would happen once she passed away. Can't find it right now; will edit this post if I do.