In the US, where Twitter & Facebook are dominant, the current consensus in the public mind is that political polarization and radicalization are driven by the social media algorithms. However, I have always felt that this explanation was lacking. Here in Brazil we have many of the same problems but the dominant social media are Whatsapp group chats, which have no algorithms whatsoever (other than invisible spam filters). I think Yishan is hitting the nail on the head by focusing the discussion on user behavior instead of on the content itself.