Steven Universe and "terrifying" are not words that fit quite right together. The show focuses on the misadventures of a young boy and his guardians, the Crystal Gems, as they fight monsters and save their city and the world. Along the way, they also overthrow a tyrannical system of government focused on eradicating individuality in order to conform to the whims of their God-Queen, the truly terrifying White Diamond.
While White Diamond, who seems to be the ultimate villain of Steven Universe seems like a drastic departure for the series in theory. She is absolutely horrific, but what makes her even more terrifying is her thematic significance in Steven Universe. She is, in essence, a terrifying representation of Steven Universe's thematic antithesis: individuality and uniqueness is a flaw that needs to be purified.
Who is White Diamond?
White Diamond is part of the Diamond Authority, a group of incredibly powerful Gems who govern the expansive Gem Empire. While Yellow and Blue Diamond often command the fleets and maintain peace throughout the Empire, White Diamond has not left the Gem Home World in centuries.
She remains a constant presence, commanding complete devotion from her subjects -- including her fellow Diamonds. She sees free will and emotion and any thought as coming through her. She sees all life as an extension of her being. As such, should she become dissatisfied, she can effortlessly take away said free will, turning a person into a T-posed extension of herself. She most notably did this to her Pearl servant, whom not only lost her free will, but also lost her very eye to White Diamond.
WHAT WHITE DIAMOND WANTS
There are, of course, several villains in Steven Universe and in fiction who want to eliminate free will from those around them. For instance, Ego the Living Planet from Guardians of the Galaxy Vol. 22 feels the world would be better if everyone was him. Ehat makes White Diamond so profoundly disturbing is how calm and matriarchal she is about it.
Rebecca Sugar is quoted on Cartoon Network's Steven Universe Podcast as saying that she drew inspiration for White Diamond after watching older shows about women where authoritarian voice overs shame women for expressing emotion or being "hysterical," finding it profoundly disturbing yet utterly fascinating.
In a similar vein, White Diamond's calm serenity is what makes White Diamond so utterly horrific. She isn't malignant or cruel, and she genuinely seems to think that everyone is making a strange fuss about wanting to maintain free will. She sees everyone else as children who need to have burdens such as "choice" stripped away from them. And she will strip that choice away, without the consent of anyone under her authority. What makes all of that especially frightening is that she has the power to do just that.
WHITE DIAMOND AND THE THEMES OF STEVEN UNIVERSE
White Diamond is even more disturbing because of how she exists to counter the greater themes of Steven Universe. The series focuses on embracing individuality and rejecting societal demands. Gem Society emphasizes a strict caste system that all the Crystal Gems, from Pink Diamond to Garnet, all reject. White Diamond is at the center of it, creating all the rules the characters break away from.
The idea of conformity and individuality exists throughout the series, with various characters coming to terms with who they are and how they can reject the systems of control that run their lives. But at the center of it all sits White Diamond, who creates structures that no one wants to follow but feel they have to.
Because she represents the core themes of conformity, White Diamond exists as the polar opposite of the warmth provided by the Crystal Gems. While acting on love or individuality is framed as warm, White Diamond's coldness and sociopathic indifference to life is framed as downright chilling, and she's not afraid to rip out souls while speaking with a cool, warm voice.