Benevolent meddling won’t help us make good decisions. We have all cringed watching friends and family make terrible decisions, and been tempted by visions of the pain spared if we could only make them follow our advice. The same feeling motivates well-intentioned technocrats to take charge of the public: People are plainly making sad blunders ...

The Panama Papers—the massive collection of leaked documents from Mossack Fonseca, a Panamanian law firm that helps set up offshore shell corporations—have already had political consequences. Iceland’s prime minister, Sigmundur David Gunnlaugsson, resigned after the leak revealed that he had partly owned an offshore firm. David Cameron, the British prime minister, is facing criticism over ...