There has to be a bad guy.
All right, that's not true. There doesn't have to be a bad guy. There is no rule that states the necessity of a heel. No statute that specifies the presence of a widely despised, shadowy, black-hatted figure who dominates the mood of the room. No understood agreement requiring the existence of someone or something toward whom a large percentage of an audience can hurl a chorus of boos.
But, man, the world sure is a lot more fun when there is one. Darth Vader, Thanos, The Joker, Norman Bates, the Wicked Witch of the West, that wizard with no nose whose name Harry Potter wasn't supposed to say aloud, and now, the 2023 Michigan Wolverines.