From Manzi’s vague article, it's difficult to figure out what he fears. But I would guess it is something like the silly 1997 eugenic dystopia sci-fi flick Gattaca. (Tagline: "There Is No Gene for the Human Spirit.")
Weirdly, Manzi argues that it would be okay to establish a scientific totalitarian state:
"Science may someday allow us to predict human behavior comprehensively and reliably, so that we can live in Woodrow Wilson's 'perfected, co-ordinated beehive.'"
Nevertheless, we shouldn't, yet, because science hasn't become accurate enough:
"Until then, however, we need to keep stumbling forward in freedom as best we can."
Well, that's a relief!
Although Manzi can't seem to find any living human beings who advocate converting American into a dictatorial scientocracy, he still spends much of his article laboriously (but pointlessly) documenting that the human sciences aren't advanced enough at present to implement Gattaca. It's a "straw man argument" raised exponentially to the point of self-parody.
My main memory of "Gattaca" is that astronaut training in the future will apparently consist of long rows of well-groomed young men dressed like extras from Brideshead Revisted typing away under the direction of Gore Vidal. That's what I remember -- lots and lots of typing.
Here's some of the film's screamingly repressed typing-centric dialogue:
Gore Vidal: "You keep your work station so clean, Jerome."
Ethan Hawke: "It's next to godliness. Isn't that what they say?"
Gore Vidal: "Godliness. I reviewed your flight plan. Not one error in a million keystrokes. Phenomenal. It's right that someone like you is taking us to Titan."
The filmmakers must have pitched "Gattaca" like this:
"It's like a gay version of 'The Right Stuff' crossed with "Mavis Beacon Teaches Typing."