I'm unsure about this class of problem. On the one hand, it most definitely
is a problem (the quote about 'engines of personalisation' being engines of radicalisation was particularly resonant here).
But on the other hand, I don't know that it's a problem to be fixed in-platform. Society has dealt with unsourced or decontextualised information in the form of gossip for millennia, and it's done that by building up an immune system of sorts, in that people (mostly) grow up knowing to take stories they hear in the pub (or wherever) with a healthy pinch of salt.
What we haven't done is start giving people chatting in pubs "citation needed" tickets. Maybe that's a bad thing - I don't know - but it seems like the real solutions to these problems all involve instilling healthy scepticism in the populace at large, and a habit of treating online interactions just the same as offline, rather than altering the medium.