I agree that debate cannot occur on social media and it would be better if no one used Facebook; leaving social media certainly sets a good example.
But I'm arguing against the sentiment that whatever goes on on Facebook is merely a symptom of politics that occurs face-to-face. We live in a world in which people can form political opinions and vote in elections without ever leaving their house.
Today, Facebook might not yet be one of "the usual attachments to society." My point is precisely that social media is increasingly seen as one of the "usual attachments," particularly among younger generations.