Good point well made. In the UK Down’s syndrome is now commonly screened for with an option for the parents to abort and there’s very few people that see a problem with that, is that eugenics?
Most people would agree “I only want a child with blonde hair” is too far, but as for preventing suffering, as you say, it’s a tough line to draw.
I just wanted to say that you shouldn’t be getting downvoted. You’ve asked a question that isn’t editorialised, appears to made in good faith and asks the opinions of others.
You’ve prompted some very good answers here.