The twitter link in the comment at the top of this post reports that the top 10 daily FB posts are almost all right wing. I am pretty sure this is being driven by a minority of users (and a lot of bots). In fact we know the whole system can be gamed. In that sense the whole network is polluted and suffering the tragedy of the commons.
[1] https://www.amazon.com/Big-Sort-Clustering-Like-Minded-Ameri...