Stealing is illegal, unless the government is the thief. On Wednesday the Supreme Court will hear a case on whether the government can seize a chunk of a business’s product to regulate prices. This is a big one.

Like much government mischief, Horne v. USDA has its roots in the Great Depression and federal programs to prop up the price of goods by controlling supply. To create raisin scarcity, the government established a Raisin Administrative Committee that manages the supply of raisins through annual marketing orders. Raisin...