Gene Roddenberry had an issue with Lt. Saavik
Lt. Saavik, played by Kirstie Alley, first appeared onscreen in the 1982 movie, Star Trek II: The Wrath of Khan. Little was known about her character even though she returned (with Robin Curtis taking over the role) in both Star Trek III: The Search for Spock and Star Trek IV: The Voyage Home. Her background wasn’t fully explored onscreen, but subsequent novels (and a deleted line of dialogue from The Wrath of Khan) indicated that she was half Vulcan and half Romulan. And Gene Roddenberry had a big issue with that point of Saavik’s background.
According to Harve Bennett in The Fifty Year Mission: The First 25 years, Roddenberry fought against the character because Vulcans and Romulans couldn’t intermarry in the Star Trek he had created. There is some confusion as to whether Saavik’s parentage could be seen to violate the continuity of the franchise, which was what Roddenberry had the most issue with.
In “Balance of Terror,” an episode from Star Trek: The Original Series, Romulans are seen for the first time, and that is when they are discovered to resemble Vulcans. Even Spock wasn’t aware of the resemblance. But that’s not to say other Vulcans weren’t aware. So Saavik’s ancestry could have been a possibility as some writers of non-canon novels have explained that Vulcans were fully aware of the Romulans’ heritage but hid the knowledge from the Federation because it was too embarrassing.
It wasn’t Lt. Saavik herself Gene Roddenberry had a problem with
But was the issue simply that Roddenberry had already established that the two species didn’t know one another, and therefore, could not be involved in such as manner as to produce a child? It seems like a small matter to argue about, but, Roddenberry created this world. He had established the rules (although they might be a bit wobbly at times), and making a change, even the smallest of changes, to a creator’s world without permission can be upsetting.
Looking at it from today’s pop culture, it might be akin to a screenwriter deciding that Harry Potter’s father was actually alive or that Bella Swann was immune to Edward Cullen’s charm. Even the slightest change to a book character onscreen can rile up thousands of fans. So imagine what that does to a writer.