Under the eye of NBC Standards and Practices and a less "liberated" American culture, Roddenberry did some great writing for Star Trek. True, he started off with a green Orion slave girl, but the rest of the series was played pretty straight. By 1979 however, when he was under far less restraint, he was again injecting off-color material into the franchise for no better reason than attention-getting.
The love instructor bit in his TMP novelization, plus Ilia's whole "overwhelming pheromones" deal, seemed awkward and stupid to me even as a hormonal teenager. I'll bet Star Trek II would have been sexed up if GR had stayed in control.
I like sexy movies as much as anyone, but that's not what Star Trek is best at, and not what I want to see Kirk and Spock dealing with.