I'm not sure filtering out or flagging up bullshit would make much of a difference.
People don't return to Facebook/twitter/etc. for a cognitive fix, they return for an emotional fix. "Trump is a conman!", "Clinton is a crook!" get the emotions going. As any reader here knows, making decisions when emotionally compromised is a bad thing. When we're all riled up, we'll eat up anything that panders to our pre-conceptions. Look at slashdot - the readership here should be skewed to a more analytical type of person, but the comment threads about say systemd are just as ghastly as Mail online threads about foreign benefit recipients.
Today, there's just no break from the emotional stimulus.
Back in the day (presumably when America *was* great), we'd get all hot and bothered by what we'd read in the morning headlines. We'd bang the breakfast table, let of steam by having a good swear and compose a letter to the editor in our heads (and sometimes put it to paper). But then, we'd get on with the rest of the day, never looking back at the paper because the headline and story were un-changing. We'd have time to come down, maybe fire up some deeper thoughts, maybe take a more sceptical view of things and generally come to a rounder decision. Now though, the headline keeps changing, we keep returning to it because it's in our pocket, pinging us with updates. Now, we can send off a comment and receive an emotional buzz with each like, share or reply. There's no escape and no point when we can step back and take a calmer look at things.
Personally, I don't really see a way out of it. Our brains are evolved to think quickly and efficiently, but not necessarily accurately. The constant emotional buzz just trains us to behave in the same way so it becomes self reinforcing. We're just not going to biologically evolve our way out of making poor decisions. Until a generation of people grow up who can limit their self-stimulation (phnarr!) and take time out to look at things dispassionately, then we're stuck - and that sort of change is a societal one.