Iceland has reduced the incidence of Down's syndrome by screening and terminating Down's pregnancies, not by medically resolving the underlying chromosomal nondisjunction. The role that social pressure plays in this process in unclear: the founder of DeCODE genetics has speculated that "heavy-handed genetic counseling" may be influencing decisions.
This is precisely the scenario that anti-eugenicists warn about, especially for more complex genetic disorders with a spectrum of potential phenotypes and possible pleiotropic effects. And for the community of non-terminated disorder carriers, who may receive less social support - and less research into medical treatments for their disorder - as a result.
Genetic screening has many great potential benefits, but the Iceland Down's example is not their best showcase.