Social media exposes weakpoints in human nature - mob mentalities, comparisons of global norms over local ones. People died and many more are likely disturbed and divided.

India comes to mind as some of the earliest worst-case examples: https://en.wikipedia.org/wiki/Indian_WhatsApp_lynchings

I buy into teen mental health tanking correlating with the rise of mobile social media in 2012: https://archive.is/frHnA

I think there's probably far more powerful but hard to describe and prove effects out there in play by connecting to a global async awareness network, but I'll leave it there.