Villains in homestuck are deeply childish adults, who are petty and immature and malicious, they throw temper tantrums when they don’t get their way. They are reflections and foils of the child player characters who they hold power over due to being adults.
The villains hold onto an edge of mystery, we aren’t allowed to see into Condy’s head outside her counterpart Meenah for a reason. Children have no way of understanding why thier adult abusers hurt them. Being a child and having an adult use thier power to hurt you is one of the most primal forms of horror.
Doc scratch and Lord English are made from characters who are thematically tied to the concept of not being able to grow up. Equius, whos character arc was cut off the moment he started to evolve, AR, an AI whos base code will always be 13yo Dirk, Gamzee, who is stunted and reduced to a plot device by the alpha timeline, and Caliborn, who stunted his growth when he killed Callie instead of predominating naturally.
Doc scratch is to Alternia what Bro was to Dave. He is the father of a planet full of children and uses his power to groom those children, under the falsely benevolent excuse of preparing them to play sburb.
Lord English is a ticking time bomb, a doomsday clock whos intentions are barely understood. Supposedly he is seeking his sister, Calliope, to kill her. In his quest to do it, he slaughters the ghosts of countless kids and teenagers. He is an overgrown child using his power as an adult to hurt the children around him.
Jack Noir is an extremely childish, immature man. He is also extremely violent, but that violence is in turn cartoonishly immature. He is a father figure, Karkat did view him as that, it was even confirmed in the book commentary. When Bec Noir invaded the trolls session, his attacks from Karkat’s point of view were that of watching his father figure suddenly turn on him for no reason.
The greatest Evil in homestuck is that of adults who abuse the children under their power, and the reason for thier cruelty is because they refuse to grow the fuck up. They are disgustingly pathetic monsters, stewing in thier hatred and cruelty, and targeting those they have power over, children, to inflict their malice.
In the metaphorical narrative of homestuck, the definition of true evil, is that of an abusive parent.
