Speaking up used to be something you do to change someone's mind or yours. What's the point in speaking up if nobody does anything with what you said?
The like button reprogrammed people. They started getting positive feedback for speaking in an echo chamber, for saying and doing things their audience already agrees with. They started getting negative feedback for doing the thing language was designed for.
Normal purposeful speech makes different opinions closer, while speech under the feedback of the like button makes similar opinions even closer and different opinions further apart.
If the interaction stays the same of course fragmentation is inevitable - but that's not a good thing. This fragmentation extends to the real world and has real consequences. It will blow up. Even with Twitter being internally fragmented the polarization in society grew. Nobody wants to listen to the other side anymore, while there's always the most to be learned from listening to the other side.
The core of the problem needs to be addressed: that social media has reprogrammed people to the purpose of speech.
One of the reasons I'm even bothering with websites like HN as opposed to social media is because it still feels like there's a slight chance of making people change their minds here.