I think it's somewhat important to ask why this effect is more observable for girls than for boys, and Haidt does not seem to really reflect on that. Social media in and of itself is really just an accelerant for the particular set of social expectations we stack on girls and women around appearance and how that relates to self-worth. Boys have more capacity to transcend social media's focus on image and beauty by fi…
They're not trying to win boys' approval, instead girls' approval.
Social ranking amidst young girls is natural behavior, what changed is that the limits of the physical world that kept it in check were removed, and now we see the fly-wheel effect.