Last week, the Supreme Court threw a grenade into years of painstaking negotiations between the family that helped usher in America’s opioid epidemic and thousands of their victims. In a 5-4 opinion, the Court held that a complex settlement worth as much as $6 billion, and agreed to by oxycontin manufacturer Purdue Pharma, the Sackler family who once ran it, and a long list of plaintiffs including states, tribes, and individuals, could...