This actually demonstrates a rather significant factual ignorance:
First of all, Down's Syndrome is not a "medically disastrous" genetic mutation, unless you take an extremely broad definition of the term "disastrous." Second, while the means of "traditional eugenics" were obviously very different from what's emerging now - involving state power rather than parental choice, and selective breeding/sterilization rather than prenatal genetic screening and abortion - the ends were the same: the genetic improvement of the human species through the scientific management of the reproductive process.
The idea that this is about "genetic improvement of the human species" is really, really off the mark. Start with Down Syndrome. Down Syndrome is a non-specific mutation. Its incidence is not predicated upon parents' heritable traits. Abort every Down Syndrome fetus on the planet, set things in fast forward, and you'll see--in proportion--an equal number of incidents of Down Syndrome in the next generation.
As for inherited diseases that result--I would imagine--in a lot of abortions (Tay Sachs comes to mind), we're almost never talking about an infant that will mature to adulthood and pass along his or her genetic disease to offspring. Whether because of death or sterility or incompatibility, there are just very, very few cases wherein the ultimate impact of the abortion is to improve the overall stock of the human genetic lode. One of the main reasons these fetuses are being aborted is that they have tragic illnesses that happen to all but destroy their reproductive fitnesses. Frankly, for somebody who waves off the idea that the right ignores science, Ross seems to be doing exactly that. I'd suggest he stick to arguments about the humanity of fetuses and steer clear of the eugenics charges if he wants to be compelling on the point of reproductive choice.