The list of "internet challenges" [1] alone should be enough to warrant serious crackdowns across the board, and that's just dangerous challenges and doesn't include other noxious effects of social media like hordes of Instagram followers ruining flower fields [2][3] and tourist destinations [4].
And hell, not just the platforms should be held accountable. Track down and arrest every single one of those utterly vile people exploiting the suffering of fellow human beings. Just because they're doing it "on the internet" shouldn't mean immunity from the law.
[1] https://en.wikipedia.org/wiki/List_of_Internet_challenges
[2] https://mashable.com/article/instagram-ruining-california-su...
[3] https://matadornetwork.com/read/instagrammers-destroying-sib...
[4] https://qz.com/quartzy/1580867/all-the-tourist-destinations-...