I wonder how familiar you are with the reality of a life with DS today. Certainly some children with DS are dependent their entire lives, but others marry, have jobs, support themselves, teach others, etc. And on the whole, both individuals with DS and their family members report higher levels of happiness and satisfaction with their lives than others.

I can say with absolute sincerity that if I happen to conceive a child with DS, I will feel like I won the genetic lottery. Not saying you do or should have the same values, but dismissing the experience of the families who do have these children in them because you have a different set of values that would make it undesirable for you isn't fair either.