Left unchecked, the technique, which weaponizes emotional data for political gain, could erode the foundations of a fair and informed society.One of the foundational concepts in modern democracies is what’s usually referred to as the marketplace of ideas, a term coined by political philosopher John Stuart Mill in 1859, though its roots stretch back at least another two centuries. The basic idea is simple: In a democratic society, everyone should share their ideas in the public sphere, and then, ...