This episode is interesting because it punctures the pretentious idea that ST presented a glorious vision of a great future for Humanity. If that's the case, then why is Dr Adams the most evil git in ST history?
The scenes with Kirk and McCoy questioning Van Gelder in sickbay are among the most disturbing of the whole series, thanks to Morgan Woodward's performance, and the horrible idea that Van Gelder is like this because of something that was done to him deliberately, and for no real reason, other than cruelty.
The episode is also a bit sick and kinky, with scenes of sweaty, raving, gibering madman Van Gelder followed by Helen Noel, in her miniskirt, black tights, and blue knickers(which are clearly on view) waltzing around in a prison for the criminally-insane! Its a shame we dont see Van Gelder after the machine has been used to return him to normal, otherwise, a great, and somewhat, grim story.