I think this is a deeply flawed interpretation of the original commenter's post. They are suggesting that we think very carefully about imposing our standards of what constitutes a "good" person on the unborn. I don't see the problem, honestly.

All analogies are flawed and I think you’re taking the wrong message here.

If doctors gave mothers a vaccine that prevented down syndrome, at a high level, that would be the same as putting an anti-down syndrome drug in the water supply.

The point of the example is not about whether putting things in the water supply is good or bad.

All of the arguments in this thread seem to be treating this research's outcome as deleting a person, and applying a corresponding moral judgement thereto. But it is not! I personally find that choosing to not have a child with Down Syndrome by engineering away the possibility in advance is no worse than choosing not to have a child at all, and better than aborting a viable but affected fetus, because no life is ended. I am not a murderer for choosing not to have any child at all because I feel that my genes should not be imposed on another generation, and I am not a Nazi for saying that if I had a child, I would take any available humane steps to ensure it received the best subset of genetic material from the set available to it. I would, in fact, argue that leaving the creation of a whole person who will have to experience life for 80 years to a series of genetic coin flips is morally reprehensible. Just because we've always done it that way doesn't make it desirable or humane. I welcome this development.

This post is about curing down syndrome though.

Saying “but they’re happy” in this context is implying that we shouldn’t try to cure it, which is obviously ridiculous.

So there’s no difference at all? Making everybody have brown hair is the same as giving everyone down syndrome?