A response to Abi's post
The characterisations of 'echo chamber' or 'filter bubble' as opposed to 'public discourse' miss the point. There is no one public- there never was. Literary theory talks about each work having a 'public', and reactions to the work having 'counterpublics'.
Thinking about the web as set of partially overlapping publics makes a lot of sense, and one of the great things that twitter did originally was accommodate that well. We followed people we were interested in, read some of their tweets, responded to some, retweeted some to our own public and so on. There was a place on the side of the stream where you could look at replies to your tweets, from those you didn't follow, but it was very much secondary.
However, Twitter misunderstood the strengths of this, and in their urge to drive engagement, packed the app with notifications. The most egregious of these was making @ replies the primary notification, and the Big Red Number on the app on iOS. Suddenly, it was another email inbox where others' priorities were ranked above your own choices.
Chasing engagement, they listed all the replies under the posts, whether you followed the people concerned or not. They had reinvented unmoderated blog comments too.
Then of course, the Tragedy of the Comments occurred, just as it has done from the dawn of time. The power to force people to see your reactions to their comments is very hard to resist, and it changes the tone of the discourse.
Now Twitter is trying to mitigate this, but blocking and muting only affects what you see, not what others see in response to your posts. So you may have a trail of abuse attached to your posts that is visible to everyone but you.
Twitter doesn't realise it needs to cherish its tummlers.