Interesting comments about Eugenics. 
The funny thing is, that in the west, Abortion for genetic issues is NOT forced, so the gov is not partaking in an form of Eugenics. As such, it is Cultural. 
However, Eugenics is practiced by all humans. Why? Because we select mates based on desirable criteria. How many women will pick a man that is a drunk or doing massive amounts of drugs, but is able to hold a job and provide for them? Few. Even Fewer will be the number that want to have a child with him. IOW, the mother has practiced Eugenics. 
Likewise, how many normal siblings of down children will decide to marry a downs adult and have a child with them? I would be willing to bet it is VERY LOW. 

It is nice that parents can look out for these kids, though they do not comment on the fact that once those parents die, who looks out for the downs kids? Oh yeah, SOCIETY. 
IOW, these ppl are counting on others do their jobs. 
In fact, how many of those with downs kids has adopted other down kids