These communities seem natural given the nature of the internet. The barrier to publishing or forming a community is pretty much non-existent, and because the internet transcends most borders the critical mass of people required to form communities with non-mainstream ideals is incredibly low. And so you get groups of holocaust deniers, flat earthers and apparently (+ unfortunately) paranoid schizophrenics.
It seems like the internet might almost reinforce the echo chamber by amplifying the feeling that everyone else is a 'sheep', because you see the big communities of people (news organizations, social media etc) dismissing your communities ideas and so people turn more inward and focus more on others who hold the same views.