[gizmondo]

The slippery slope scenario you described didn't happen with the Down syndrome for which there is a reliable screening. There are a few people want to ban that screening and they use exactly the same arguments (also it's eugenics!). We're lucky that at least these people are rightfully viewed as insane.

[immibis]

How hasn't it happened? Is there government support for parents of Down syndrome children?

[didibus]

There is Supplemental Security Income in the US. And I think in Canada and Europe there are even more government subsidies available.