This is not an attitude exclusive to progressives. The chief grievance here is that the historical “solution” to the “problem” of Down Syndrome has been abortion. Opposition comes from the pro-life movement (which is generally conservative) and disability advocacy groups (which are generally liberal).

A novel therapy that does not result in the termination of the pregnancy might satisfy the conservatives, but it does nothing to satisfy the disability advocates, who point out that these kinds of technologies fundamentally normalize the idea that they should never have been born the way that they are.

“Fundamentally normalize” is the part that surprises me. I sometimes think that it is the refusal to hold two thoughts simultaneously that drives it.

One can value/respect people with DS and strive to eliminate DS at the same time.

Hailing from a particularly conservative country I can tell you right now that it's not going to satisfy the conservatives, as their core belief is that the world is zero-sum and tampering with that, in their view, wrong.