New Delhi, Aug. 17 -- In a federal courthouse here Monday, the attorneys for four states stood before a judge and argued something that would have sounded improbable a decade ago: that the features designed to keep teenagers scrolling Instagram and Facebook constitute an unlawful product, and that Meta Platforms must pay for the harm those features caused.

up to $1.4 trillion in civil penalties. The actual argument was narrower and, in some ways, more unsettling. Not that social media harmed children as an unintended consequence, but that Meta's engineers built features with a calculated understanding of their psychological effects and then withheld that understanding from regulators, parents, and the public.

Four state attorneys genera...