We disavow social media platforms as public squares because the implications of such a view are not great. I've spoken of this elsewhere, but a similar phenomena happens with treating social media as the source of our contemporary social ills: it literally elides the fact that we've been living in a dream world.
By this I mean, we assumed that we were a civil society with mutual respect, but what social media has revealed is that this is not the case, that this is far from the case.