On ideological echo chambers

Allegedly the internet has created a political culture where individuals place themselves inside an echo chamber where they only share ideas they agree with and are exposed to ideas they agree with. This clearly has a ring of truth to it, although I have found upon closer inspection that the overwhelming majority of posts are sharing the worst of the other side. Most of the left-wing echo chamber consists of echoing the most obnoxious right wing propaganda and vice versa. This seems intuitive and reasonable too – look at yourself. Do you feel more comfortable standing up for a particular positive position that is definitely the right way, or just pointing out Nazis are bad?
Unfortunately, the straightforward result of this would obviously be a social media ecosystem where the political memes most fit for survival are those which can be best held up by the other side as the most preposterous.
I strongly suspect that this, and this alone is responsible for the alleged polarization, insanity and extremism in political culture in the last 10 years.