During the Nazi regime, written records of people’s religious affiliation were used to target and detain Jewish individuals. I know it’s far-fetched in the current world, but there is little defensible reason for corporations (or governments!) to hold that much information about individuals.
It’s also been documented that lack of privacy has a chilling effect in public discourse, whistleblowing, and other activities where you’d expect a reasonable level of privacy.
It’s not 100% privacy vs. none, but at the moment Facebook and Google are both very, very close to ultimate knowledge about an individual.