But social media is part of our life as a whole, we are a social species. If our mental health had a net decrease as a whole on the whole society, yes, we could throw stones as social media as the author wants.
But for that we'd need to first include assesment of absolutely everything touching social media and look at the net result. Doee it improve family communication? Does it help or hurt social discourse ? Does it help or hurt minorities ? What's the impact on social mobility ?
IMHO social media is just a catalyst of our social trends and while the lows are really low, the highs can also be incredibly high.
I'd be more sympathetic to an argument about raising the floor to cut te more toxic behaviors than just try to isolate it in an "adult only" corner and pretending the situation got better.