Haidt's case rests on four harms he says smartphones and social media inflict on the developing adolescent brain: social deprivation (screen time crowding out in-person interaction), sleep deprivation, attention fragmentation, and addiction — the same compulsion loops DarkBadge scores app by app. Puberty, he argues, is a sensitive period for social learning, which is exactly when a phone-based childhood does the most damage.
The book is also prescriptive: four norms — no smartphones before high school, no social media before 16, phone-free schools, and far more unsupervised free play — that only work, Haidt says, if adopted collectively rather than by one family alone, since a child's whole peer group being online is what makes opting out feel costly.
For DarkBadge: The Anxious Generation is the clearest lay case that the harm isn't a personal-willpower problem but a collective-action one — which is the same framing behind scoring apps publicly rather than asking users to police their own use.