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.
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.
Everyone says they want free speech. But deep down they don't. Some don't want gay marriage written in books, and some don't want anti-vaxxers to post misinformation. Those are 2 sides of the same coin.
Freedom of speech is a critical cornerstone of liberal government. The fact that so many sides want to reduce this right is what is scary.
We have much less freedom than we think, and the freedom we do have we pay a very high price for. I often use the phrase "What price freedom?" in conversations, and unfortunately most don't understand what it means.
1. Your freedom can cause problems to me an to society as a whole
2. We pay much in blood and treasure to maintain our freedom
3. There are unintended consequences and knock-on effects to most all rules regarding freedom.
Or to generalize: "Freedom isn't free"
The same paternalism has justified poisoning one's own people in a "war" against alcohol, dictated who was allowed to have sex with whom in privacy of their own home, and resulted in human experimentation for the supposed betterment of society.