I think euthanization is overkill, but maybe sterilization would be better. I don't know.
It's a tough call, because while we know so much about the human genome, there's still so much left to learn.
Do you know that Africans who are carriers of the gene that causes sickle-cell anemia are immune to malaria? That's why it kept on and keeps on getting passed down. The people who have both copies of the sickle-cell gene die from complications of the disease. The people without any copies of the gene die from malaria. The people with only one copy, who carry the disease but don't show symptoms, are the ones left to survive and reproduce.
They just found something similar with the gene responsible for cystic fibrosis, if I remember correctly. That explains why it's still being passed down.
So yeah, it's a really tough call.
