My pet theory is that social media isn't the problem, the always-on surveillance created by smartphones is.

When I was in university, we had nude parties. I'm pretty sure nobody would risk that nowadays. That cherry-picking you mentioned goes both for highs and lows. In this day and age, you always need to plan for your worst moment to end up in someone's picture. The ubiquity of cameras has made everyday living more risky in the sense that you're constantly at risk of losing social standing over insignificant mistakes.