Twitter has changed. When it started out it was a haven from the unread count in your email inbox, from the tension of blogging and comments. You didn't have to write long form essays, you didn't have to moderate commenters. You didn't have to make all those bold lines go away to reach inbox zero. You just followed some people and typed thoughts that occurred to you. Those who followed you got texted them, or sent them in IM. Simple.
Then, we came up with @ replies. They were a way of making it clear who you were responding to. Twitter sensibly adopted them, but they were off to one side. You had to click on the @ tab to see them. Your primary experience was still the people who you followed, which you controlled. I wrote about Twitter theory with this in mind.
Twitter reinforced this by hiding tweets that start with an @ unless you followed the person being talked to. This reduced serendipitous friend discovery, but also damped down arguments. (You can still see this in twitter analytics: note the difference in reach versus engagement for posts versus replies).
However, Twitter had a perceived problem - this very contained, comfortable nature meant that it took effort to get started and find people to follow. They worked really hard at changing this, building a sign up process that made it very hard not to follow lots of people, especially famous ones. Also, they changed the way we got notified.
Emails and app notifications of new followers and @ replies were set up to drive engagement, encouraging you to return. That @ tab got an unread count on it, just like the email inbox, and the app got a red number on it on iPhones.
The problem with this is that responses do not follow a smooth distribution. Sure, most tweets get no responses, but some take off. Hashtags became another way to spread tweets sideways, beyond the follow graph.
Twitter saw this as increased engagement, and most of the time it was good. They built special tools in for "verified" users—the celebrities and brands they used to woo the rest of us with on sign up. The Verified get to damp down the notification flood, or just see other verified people.
The problem is that by making @ replies the most visible part of the app, they'd brought us back to email and blog comments again.
Your tweet could win the fame lottery, and everyone on the Internet who thinks you are wrong could tell you about it. Or one of the "verified" could call you out to be the tribute for your community and fight in their Hunger Games.
Say something about feminism or race, or sea lions and you'd find yourself inundated by the same trite responses from multitudes. Complain about it, and they turn nasty, abusing you, calling in their friends to join in. Your phone becomes useless under the weight of notifications; you can't see your friends support amongst the flood.
Twitter has become the hate speech wing of the free speech party.
The limited tools available - blocking, muting, going private - do not match well with these floods. Twitter's abuse reporting form takes far longer than a tweet, and is explicitly ignored if friends try to help.
This is where we are now. There are new attempts to remake following-focused semi-permeable publics. Known, ello, Quirell are some. In the indieweb world we are just starting to connect sites together with webmentions, and we need to consider this history as we do.