But that's an argument against Facebook in particular, not against social media as a category.
Fundamentally, the problem is that we have allowed the modern "public square" to be in these spaces entirely owned by private companies.
What we really need is an open protocol for a federated social network that works very much like Facebook (so, not something like Mastodon, which is designed to work like Twitter, for instance—though it would probably be worthwhile to do the same with it) and have the government operate some public "reference servers" that anyone can join, while others can also operate servers that can federate with them. That way, you're still able to connect to people even if they're not on your particular server...provided they don't belong to a server that's been blocked from federation due to hate speech or something.
This immediately puts massive scale social media in a very unique place. By contrast, public school libraries are anything but a monopoly. If they don't offer a book you want, there are countless other ways to get it that are no less convenient, to say nothing of the digital age and searching for 'book i want pdf.' This generalizes to other scenarios as well. At one time it was believed that private businesses out be able to restrict employment or service based on things like the race or religion of their customers/applicants. But as this started to become a more substantial issue in terms of scale, society decided otherwise.