Even if you don't take into account the harm of things like the Manosphere, social media is inherently harmful in its current form.
The people who built the algorithm literally studied how to create the same neurological symptoms that addicts experience.
In addition to that, it also actively harms your attention span and cognitive abilities.
And in addition to that, being bombarded with so much information all the time (whether positive or negative) is not something our minds were meant for either.
If you listen to interviews with heads of these silicon valley companies, they send their children to specific schools that do not allow technology, and they do not allow their children to use tablets, smartphones, etc until age 16 at least. And when you look at studies, those students have higher cognition and perform better than students at other private schools that do allow tech in the school/classrooms.
We've still not put enough regulation on the internet as it was pre-social media to combat the harmful parts of it, so we are way behind with Social Media, and now with AI.
Social media in of itself is not necessarily a bad thing, but the way it is used and structured right now, (as a machine to make as much money as possible) is absolutely dangerous and toxic.