I remember watching Twitter during the 2009 election protests in Iran as people from all over the world chipped in to help the protesters organize and even dodge pro-government militia and police as they were running for their lives minute by minute. I knew about the shooting of Neda Agha-Soltan before major news media did, and I didn't learn anything new from their later coverage.
During the encampment phase of Occupy in 2011, I followed live updates from protesters all across the country, mostly on Google+. Watched and chatted on livestreams of crackdowns that the news wouldn't or wasn't allowed to cover, or would blatantly lie about when they did.
I saw the videos of police shooting Oscar Grant in the back before the news began reporting it, and was able to call bullshit on their deceptive cuts of the footage, along with claims that he wouldn't stop struggling or that the officer involved looked shocked and remorseful after he was shot.
I agree about complex or divisive events, but those will always be the same thing either way. You have to get information from both perspectives and draw your own conclusions. But I've already covered that.
Why will always be a matter of dispute between people with agendas, but at least social media isn't build completely by people who are professionally trained and funded for information control to push their version of Why.
Yeah, there are professionals hired to work social media, but they can't control the story as it's happening. And the great thing about the internet is you can go back after the fact and to the earliest timestamps possible, and then watch how people try to change the details from what was plainly recorded after the fact. You can learn a lot just from that.