Social media is the largest single factor in collapsing birthrates. Social media made widely accessible depictions of lifestyles that glorify wealth, travel, living carefree lives. This increased the baseline expectations people have of their own lives. Children are just an impediment to that lifestyle. Social media also massively raises the expectation of the costs of raising kids. It's no longer enough to keep them fed and clothed. A child's existence must be maxxed in terms of attention, simulation, enrichment, etc. Anything less is deemed borderline abusive.
Facebook claims 3 billion MAU, which is basically half of the world's non-China population. Social media is the major way in which "public opinion" and culture gets formed.
Anti-fertility memes arent contained to social media, but are spread widely due to social media. Think small-world network dynamics. We're well past the point of there being a meaningful online/offline distinction (or on/off social media).
