Confirmation bias and Activism

Lots of examples showed that social media has changed the world. #MeToo, #BlackLivesMatter, and many things that I don't know but now changing the world with the power of social media.

How could people change the world using social media? Of course, they used the power of social media. Then, where does the power come from? Of course, social media connects individuals and helps them to build their own networks. 

Then, how certain information about a single event that can trigger the whole thing can spread over the networks? There might be lots of mechanisms, but one factor might be people's confirmation bias. I do not want to be too cynical, but that is why two different parties are still fighting on the networks, arguing certain topics (e.g., Roe v. Wade).