The mood and chemistry of the whole thing was all just wrong. If they had gotten a playful mood, or some real chemistry with the actors, it might have worked as sexy, but they hit all the wrong notes. It's not just about the gratuitous panty shot, it was all in the execution. Done in a different way the same amount or more of flesh could've been exposed and I wouldn't have found it objectionable.
Right. The criticisms of the scene aren't a prudish reaction to the presence of skin, they're a recognition that it was done awkwardly and poorly, in a way that served neither of the characters well. If the intent was to hint that Jim Kirk and Carol Marcus have a future as a romantic couple, then it failed in that regard, because it played more as creepy voyeurism than mutual attraction.
Roddenberry may have insisted his actresses show a lot of skin, but at least he never made it seem that the characters were uncomfortable with the exposure or that the male characters were ogling them without their consent. He pandered to male gaze, but at least he let the female characters show off their bodies willingly and without shame. Even in the raunchy sex comedy film he produced and wrote, Roger Vadim's
Pretty Maids All in a Row -- in which Rock Hudson plays a high school guidance counselor who sleeps with his underage female students, essentially a serial statutory rapist -- all the nude scenes feature female characters who are quite happy and eager to disrobe in private for their male observers, and the one scene where a man does voyeurize an unconsenting girl (when inept cop Keenan Wynn barges in on Hudson and one of his paramours in a parked car) portrays the man's invasive gaze in a negative light. Plenty of later high school sex comedies made male voyeurism of unconsenting girls a standard trope, but Roddenberry didn't go for that. He sexualized women like crazy, but always gave them agency as well, portraying them as active and consenting participants and frequently as aggressors. He wouldn't have hesitated to include a scene wherein a female character stripped to her underwear to seduce Kirk,
but I don't think he would've included a scene where Kirk leered sophomorically at an underwear-clad woman without her consent.