I have people in my family with Downs. It made the early pregnancies for every one of my children a terrifying ordeal. Luckily my children were all born perfectly healthy.
I love my family members with it, but their lives have been so much more difficult than they needed to be. It’s not just massively difficult for the disabled, it financially ruined their parents and their care is also a massive tax burden on the community.
If we can eliminate a crippling disease by “just” turning off a gene we should absolutely do it. The alternative is aborting them as soon as it is detected, and even then it isn’t always caught in-utero.
I have worked with people will all sorts of disabilities my entire life. I can confidently say that if I asked any of my blind or deaf colleagues that if they could take a simple gene therapy so they could see/hear again that they would do it without hesitation. Why would Down Syndrome be any different?
I can’t think of a single valid argument against it other than “eugenics bad”. We aren’t talking about Nazi-era human experimentation here.