A lot of commenters here are mentioning that better education could help solve this problem. I agree. What if there were a new type of "teacher" who replaced or augmented regular mods on sites like Reddit? Universities strive to hire professors who will teach students to be open-minded, consider the sources of information, and just think better in general. The prestige of each university is largely based on this fact…
They turbocharge group think. Probably not the best example of an open minded community.
A distant cousin of my wife went to a Seminary; within a relatively narrow range of beliefs, he claimed there was a lot more intellectual freedom than universities along the lines of teaching how to talk to devil's advocates and heresies and converting non-believers. More of a carrot and stick than university which is solely stick-style, who can most emphatically say "I can't even" and so on.