Substack is now asking for age verification using Persona, which is great(?) if you want to give your biometric information to a Peter Thiel-backed company. Thiel famously also owns controversial surveillance-enabling company Palantir.
Five years ago I wrote the following about Biometric Abuse as one of the elements of digital ethics. It's extremely worrying how easily it's collected, and how little guidance there is (from a societal perspective) for understanding what you are actually giving away to a private company and how that may harm you.
Biometric abuse
Collection of biometric data is on the rise while neglecting the permanence, and thus immense delicacy, of this data. Once lost biometric data can rarely be reclaimed, and it can be used to identify even where anonymity has been promised. The continuous collection of vast amounts of data about humans are creating biometric markers where many did not expect it: beyond fingerprints, face recognition and gait, there is already use of heartbeat recognition and keystroke biometrics.