It's The Liberty, Stupid

I suppose it'll please Ross on some level to know that insofar as one is prepared to try to expand the concept of "eugenics" to include a world, like the one depicted in Gattaca, where "there is no state coercion of reproduction or forced sterilizations of minority groups" then, sure, the predominant principles of the mainstream American left favor that sort of thing (Ross suggests that, maybe, we call it "Gattagenics.")

The issue here is precisely that a certain strain of back-in-the-day progressivism was extremely hostile to civil liberties. You saw that in Woodrow Wilson's administration where Attorney-General Palmer led a domestic crackdown that made Al Gonzales and John Ashcroft look like ACLU members. And, indeed, it was former political allies of Wilson's who became horrified by what progressive politics turned into during that period who founded the ACLU (Paul Starr tells this story well in his Freedom's Power). Along the same lines, liberal turned against the eugenicist strain of progressive thought for reasons of individual liberty and autonomy, rightly rejecting the eugenicist movement's vision of society as horribly authoritarian and intrusive.

Flash forward through the decades and what you have are a lot of liberals who, precisely because we, like the opponents of eugenics back in the day, believe in individual liberty in the matter of reproduction, are willing to let individuals freely choose to do certain things that resemble things eugenics proponents may have wanted to force people to do. That coercion or lack thereof, however, is a crucial distinction. In the film Gattaca, meanwhile, they cheat because even though there isn't coercion around reproduction per se, you're watching a movie about a highly illiberal society where people seem to have no privacy rights, etc., and the results naturally raise hackles.