It's none of my business, but the folks that bug me are the ones that don't believe in birth control, which is OK except that as they keep having kids, and, as they get older, the odds are vastly higher that eventually one will have T21 or other birth defect. Then they have a whole house full of kids and a special needs baby. Hell, by the time someone has had eight kids, one is probably going to end up in prison,. The benefit/risk ratio of large family size drops off really fast, not just for the parents but the other kids as well, assuming low infant and child mortality .
If Darwin's son had Down's, he could have also had the heart defect that is commonly associated with the condition. Today it is repairable.. The other concern is early onset dementia around age 50.