I see it as a double-edged sword - like pretty much any form of human communication. The upside is that you can communicate with people across vast distances instead of just the people who live near you. This can expose you to different points of view. Perhaps I'm for something since I live in Upstate New York but haven't considered the repercussions to someone living in Montana. In ages past, I would have never spoken with that person and never even considered their opinion. Now, I might see their view and reconsider my support.
The downside is that you can wind up surrounding yourself with people who agree with you. This happened on both sides of the aisle during the last election. If someone expressed support for Trump, some Hillary supporters would unfriend them. If someone supported Hillary, Trump supporters would cut them off from their stream. The end result is that you just see people supporting your candidates and causes. This leads to dismissing the other side out of hand and even exaggerating their position to an extreme. (For example, "expand background checks on guns" becomes "THEY WANT TO TAKE ALL OUR GUNS AWAY!!!!")
It should be noted that this isn't unique to social media - my father isn't on social media and surrounds himself with "news" from Fox, Hannity, Limbaugh, etc. He doesn't listen to CNN, MSNBC, etc at all - even in an effort to see how different stations spin the same news. He's in a bubble and refuses to listen to anything that originates outside of his bubble.
The other downside is that people tend to be more brash online than face-to-face. If you called someone an idiot and a traitor to their face simply for having a different political opinion, you'd risk a punch to the face. Online, though, the worst you'll get is named-called right back and blocked. What's worse is that it seems like this brazenness is leaking out into everyday society (at least for some people).
In the end, I don't think there's an easy fix. There's no way to keep the good aspects of social media (and the Internet in general) while forcing people to be civil and to not stay in bubbles. You can ask people to behave in certain manners and perhaps even encourage it in some ways, but no system will be perfect. They will all suffer from the flaws inherent in the fact that the users are human.