The ultimate goal of the anti-eugenics movement has to be to build a society, to build the legal and political and economic and cultural and material conditions, in which eugenics is no longer a rational choice.
I often compare disability/class/age-based eugenics to sex-selective abortion. Banning sex-selective abortion does not solve the problem; it just violates people's bodily autonomy, builds parental resentment of their children, and compounds the misogyny that leads to the demand for sex-selective abortion in the first place.
People practice sex-selective abortion because having a child AMAB is more beneficial to the parents' social and economic standing than having a child AFAB. The solution to that problem has to be changing those social and economic conditions so that a child's gender or AGAB has no bearing on their parents' social and economic standing -- so that sex-selective abortion is no longer a rational choice in response to the parents' circumstances.
And the only way to prevent disability-selective abortion is to make disabled people so socially and economically equal to abled people that disability-selective abortion no longer looks like a rational choice.
The only way to prevent economic/class eugenics is economic equality. The only way to prevent age/status-based eugenics is social equality.
This is the main impetus that drove me to socialism. I used to be more of a center-left social democrat; I figured "Complete economic equality would be nice, but it's a pipe dream; the important thing is that everyone. It doesn't really matter if the CEO is richer than everyone else, as long as no one is hungry or homeless. Besides, it's kind of 'fair' in a way for people with more specialized/demanding jobs to be compensated more."
But the thing is, as long as inequality exists, parents will want their children to rise to the top of the hierarchy. As long as inequality exists, parents will want to prevent their children from falling lower in the hierarchy. As long as inequality exists, parents will do anything to coerce and pressure and abuse and modify their children to give them a "competitive edge."
And as long as inequality exists, and certain physical/cognitive traits correlate with "success," choosing children with those "successful" traits will be a rational choice.
Americans in disability liberation discussions tend to blame our country's ableism on our lack of social safety nets and universal healthcare... but countries with robust social safety nets are just as ableist as we are, sometimes more so. The abortion rate for fetuses with Down Syndrome is higher in Iceland than in the U.S., even though an Icelandic child with Down Syndrome would have access to healthcare. Iceland, while deeply flawed, has a decent enough social safety net that someone born with Down Syndrome would probably not starve or be homeless. But they would be at the bottom of the social hierarchy. There is still a social hierarchy. Eugenics is still a rational choice. Changing that behavior requires changing the social hierarchy that values so-called "general intelligence" and devalues disabled people.
The same is true of other kinds of eugenics -- as long as raising children is a net financial loss for families, avoiding having children "you can't afford" will remain a rational choice. As long as having children means a decrease in the birthing parent's educational or professional opportunities, people will avoid giving birth to children they "can't afford."
And of course, complete social and economic equality is still a pipe dream. Some people will always be more popular than others. Some talents and abilities will be more valued than others. But the goal has to be complete equality, or else eugenics will continue to be a rational choice.