When Gene Roddenberry created Star Trek, he had a particular way he wanted things done. He wanted the characters to be written a certain way for them to grow into the characters that we now know and love. And he wasn't willing to back down from what he knew Star Trek could be, especially since it was something that had never been done before.
When the series was just getting started, Roddenberry was adamant about the type of stories he wanted to be included in Star Trek as well as those he didn't. According to The Fifty Year Mission The First 25 Years written by Edward Gross and Mark A. Altman, Roddenberry admitted that during the first year of Star Trek, he rewrote everyone's scripts...even his best friends. That, according to Robert Justman, caused a lot of bruised egos as no writer wants to be rewritten.
But these Trek characters had never been written before, and Roddenberry had to build these characters from the ground up, and as he said, "the whole thing was in my head, and I couldn't say, 'Mr. Spock, write him like you would write so-and-so' because there'd never been anyone like that around." So when the scripts came in, Roddenberry reviewed every one, and because he knew how he wanted Mr. Spock and Captain Kirk to be onscreen, he rewrote every one of them. And he lost friendships because of it.
Writer John D. F. Black admitted that he didn't like Roddenberry, who had rewritten his script for "The Naked Time," but he went on to say that Roddenberry was "right about the characters," as well as a lot of things. And that made sense, considering Star Trek was Roddenberry's idea from the beginning. He knew what he wanted, and he was willing to sacrifice what it took to get the story he wanted made. Unfortunately, those sacrifices involved friends who couldn't handle their work being rewritten.
But Roddenberry stood firm, and because of that, we got Star Trek: the Original Series, a phenomenal series that spun-off into other series and movies and an entire franchise that has legions of fans. That might not have happened had Roddenberry backed off and let others write the characters how they wanted to write them.