Disney and its lawyers from Arnold & Porter have been handed a setback in one of the more ill-conceived lawsuits I can recall: Going after people who dress up as Disney-owned characters like Elsa from “Frozen” or Chewbacca from “Star Wars” to perform at children’s birthday parties.

It’s not just that the legal argument is weak. Or that the suit makes Disney look like a jerk. But as anyone who has ever planned a children’s birthday party could tell you, it’s also a dubious business move.