"In any other area, the left would look at a history like this and ask whether those formal convictions are the only thing that matters, or whether the eugenic past..."

"... still exerts a structural influence on the present. And in any other area of policy [Clarence] Thomas’s point about how legal abortion appears, in the aggregate, to act in racist and eugenic ways would be taken as an indicator that something more than just emancipation is at work. Yes, in their theoretical self-conception, pro-choice institutions are neutral custodians of the right to choose. In theory the genetic-screening industry exists only to provide information. In theory the high abortion rate in black America is just the result of countless individual decisions. But in practice, liberal technocracy still has a 'solve poverty by cutting birthrates' bias inherited from a population-panic age, and abortion-rights rhetoric still has a way of sliding into Malthusian fears about too many poor kids in foster care. In practice the medical system strongly encourages abortion in response to disability, with predictable results. In practice... the disparate impact of abortion on black birthrates is shaped by that reality and others, not just by free choice."

From "Clarence Thomas’s Dangerous Idea/Does anything link the eugenics of the past to abortion today?" by Ross Douthat (NYT). There is this idea in constitutional law that you need to pick one approach to interpretation and use it consistently, across all the issues, and that's what keeps you deciding cases according to law and not policy preferences. An argument can sound completely cogent, but if it's not the kind of argument you always make, it's a lawyer's argument, not a judge's reasoning. Of course "the left" are political actors, entitled to make their lawyer's arguments, and they may not be embarrassed to find themselves switching approaches to constitutional law to use whatever works best to get the outcome they want. It's another matter to show that Clarence Thomas changes his interpretive method this way and that, but there's no practical need to reach Clarence Thomas on abortion rights. You only need 5 to win, and he's the least likely to be in the left's 5. They only need to keep 5 of the remaining 8 away from the Thomas position that — talking about eugenics — seems designed to lure lefties to the right on abortion.