Kirk showed the way. Then they decided that they had to 'civilize' Trek. Even though Trek is supposed to be roughly Captain Cook exploring the Pacific in Outer Space.
TOS was a rare example of Executive Meddling gone right. The whole Western in Space theme of the series was all thanks to the producers telling Roddenberry that what he wanted wouldn't sell, and even toning down his vision nearly bombed TOS. The series only really rebounded thanks to reruns, its initial showing had very poor ratings.
If you really wanted to see Roddenberry's unfiltered vision for Star Trek, go watch seasons 1 and 2 of TNG. You know, the Trek no one wanted to watch, hence Paramount coming down hard on the producers to tone down the Commie propaganda BS. And even then, it wasn't until they completely got rid of Roddenberry and his craziness that Star Trek really began to shine. And not just DS9, but also
Wrath of Khan,
The Voyage Home, and of course,
The Undiscovered Country.
EDIT: No, really. Roddenberry admitted in an interview that the Federation as he envisioned it was supposed to be an idealized version of the Soviet Union. He also threw a fit when he saw the redesigned Starfleet uniforms for Star Trek II to VI, since they were too militaristic, and was about to file a lawsuit against Nicholas Meyer for Star Trek VI's 'end of the Cold War' themes when he died.