Well I think it's a matter of "is it ethical to bring into the world a being who is more likely to have a bad life or lots of suffering?" Once the person is here we are of course obligated to treat them with compassion. BTW, I'm not saying this is my view on DS -- I have met many people with DS who seem to have rich or rewarding lives. But I think clearly some people think that way. Plus, I think parents who have a child with DS are headed down a road of having someone that needs a lot of care for the rest of their lives. I can't blame someone for not wanting to take that on.