A recent Washington Post column by Ruth Marcus is titled "I would've aborted a fetus with Down syndrome. Women need that right."
Marcus's attitude is far from unusual. A large proportion of human beings diagnosed in utero with Down syndrome are killed for that reason. Many people—especially those who have Down syndrome or family members with Down syndrome—are rightly offended by this form of discrimination. It's discrimination that is made possible, however, by a prior form of discrimination.
After all, Marcus doesn't think that killing adults who have Down syndrome is permissible. She wouldn’t choose to execute a Down syndrome toddler because he is "not the child I wanted."
But that's exactly why she says she would have a fetal human being executed.
The difference is that, as Marcus puts it, she doesn't think "abortion is equivalent to murder, the taking of a human life." (Presumably, she means "human life" in a non-scientific, philosophical sense.) She doesn't think unborn human beings (disabled or not) matter in the way that older human beings matter. So, unlike other members of the species Homo sapiens, embryos and fetuses lack a right not to be intentionally killed.
It could be because unborn humans don't have the same cognitive functions that we do. It could be that they look different. It could be that we feel differently about them.
Whatever the particulars of the view, though, a decision to kill a baby on the basis of disability (or other morally trivial characteristics, like sex) is only possible because of a prior judgement that human beings at this stage simply have no human rights we are bound to respect. It's only possible because of prior discrimination on the basis of age, or size, or function, or dependency, or the desires and decisions of others.
It's discrimination on top of discrimination. It's ableism that is culturally and legally acceptable because of ageism.
But the latter form of discrimination isn't any better or more morally justified than the former. The fundamental problem with the practice of Down syndrome abortion is the same as that with abortion in general. Abortion always is a denial of human equality.