I think you make a salient point.
Historically, news either remained local and did not propagate, or if it did, it propagated slowly, and thus the impact was diffused, largely inhibiting reactionary movement.
Now, we not only have instantaneous hypersensationalised global media, but the filter-bubble echo chambers of social media which amplify and distort events to fit their world view and agenda, whatever that may be.
It's sad, really, as once upon a time we believed the Internet could bring global unity - but rather, it has deepened divisions, pushed political thought to extremes (defensiveness is one hell of a drug), and has brought about much of the societal ill we now see in developed countries.
Is there a solution? Facebook seem to be trying to break people out of their bubbles, but the thing is, people like their bubbles, as they're safe and cozy and they don't get angry at what someone they disagree with wrote.
Now, I'm pretty sure this same argument was espoused about handbills and movable type, and we demonstrably survived print, but again, velocity is the killer. I'm not sure if it's different or not.
Either way, it's the old tribal instincts doing their thing - either we need to collectively adapt (more easily said than done), or we need a technical or legal solution.
Legal solutions take the format of restrictions on speech, which nobody wants to promulgate, technical solutions will be worked around.
So - it's up to us to try to be better, to try to be moderate, to try not to get pissed off.
Maybe the solution is pharmaceutical. Maybe we need Huxley's soma. I don't see how you can change human nature quickly enough otherwise.