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This is from a 1980 interview TOS Season 3 Producer Fred Freiberger did with Starlog Magazine (Issue 39)
Starlog Magazine: [David] Gerrold also criticized the lack of a racially balanced crew on the Enterprise.
Fred Freiberger: Nonsense. The second or third show I did starred France Nuyen, who is an oriental (“Elaan of Troyius”). We did “Let that Be Your Last Battlefield,” about racial prejudice. Sticking to this racial thing, if we were going to other planets, seeing black people there would be kind of nutty, right? We would see green or blue. It wouldn’t be science fiction if they were black.
If you’re talking about a show where you have six or eight format characters, you’re talking about putting some guy who is black in a Star Trek uniform in the background somewhere? A part that has some meaning, that’s something else again.
Freiberger’s totally brushing off the issue and attempting to defend TOS’s record kind of blew my mind. This was 1980. He could’ve easily said, “We could’ve done better”. But no…
You can read my review of “Elaan of Troyius” to see why I think it’s anything but racially progressive.
The excuse about how it wouldn’t have had “meaning” to put more visible minority actors in the background is similar to what later creators said about why they didn’t have gay or lesbian background characters. Since the alternative was no diversity in background or “meaningful” roles, I’d say it would’ve still been an improvement.
More than that, how incredibly ridiculous is his argument about why black people can’t play aliens because viewers expect our aliens to look more alien? I’m assuming he forgot the numerous episodes that feature white people as “aliens” distinguished by little more than different makeup and wardrobe (and the white people playing Native Americans in “The Paradise Syndrome”).
Let’s take a look at “aliens” in Freiberger’s Season 3.
Behold the Eymorg from “Spock’s Brain”:
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The Romulans in “The Enterprise Incident”:

The white people-in-brownface Klingons from “The Day of the Dove”:
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The Fabrini from “For the World is Hollow and I Have Touched the Sky”:

“The Empath”, supposedly an alien from Gamma Vertis IV:

The Platonians from “Plato’s Stepchildren”:
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The Scalosians from “Wink of an Eye”:
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Losira, a Kalandan from “That Which Survives”:

The Gideons in “The Mark of Gideon”:
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Zarabeth, a Sarpeidon from “All Our Yesterdays”:

The Ardanons from “The Cloud Minders”:
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And a Tiburonian and a Catullan from “The Way to Eden”:

So according to Freiberger, white people with wigs and eyeshadow = believable aliens. But black people as aliens = nutty.