> 99% of people with Down syndrome were happy with their lives;

I don't believe this number for a second, but let's just assume it's true. Why does that matter? We know from an abundance of research about both the Disability Paradox and that specifically people with intellectual disabilities which are common comorbidities with Down's Syndrome express elevated levels of happiness compared to the general population in part because they lack the necessary faculties to understand their situation. "Ignorance is bliss."

Arguing against a cure that could happen shortly after birth for a debilitating disability on the basis of people reporting high levels of happiness is patently absurd.