Keep in mind a lot of this was held back by the racial politics of the era. Famously, Kirk and Uhura had TV's first interracial kiss, with a lot of hedging -- they were mind controlled (or something, I forget the details), and Shatner and Nichols only pressed their cheeks together away from the camera, so the kiss itself was phony. Still, only a few years earlier, when Eartha Kitt replaced Julie Newmar as Catwoman on the Adam West Batman, all sexual tension between her and Batman abruptly ceased. Baby steps!