Steal a loaf of bread. Is the shopkeeper you stole it from, who says the loaf costs $2.50, a "legislator"?
If the shopkeeper says the loaf of bread was worth $200K and the the court doesn't question the amount because the shopkeeper has been billed $200K for replacement of said loaf according to a contract with the bakery, the shopkeeper and the bakery have legislated the punishment for the crime.