It doesn't have to be "not free speech" to be deleterious, that's an insane argument.

A large part of how human settle on opinions and beliefs is by inference from what and how often is said around them, calibrated around in-person interactions.

Social media warp this horribly both through algorithmically selecting what information to present users with, and through impersonal "big account->user" that remove the stakes normally present in in-person communication, which completely breaks our perception of how important statements actually are.