Twitter is suffering from a systemic harassment problem. This isn’t news—it’s been written about over and over again, and has become a trope in the cultural mainstream. “We suck at dealing with abuse and trolls on the platform, and we’ve sucked at it for years,” the company’s CEO wrote in an internal memo last year. Recently, Paul Ford summed it up : “Google has search. Facebook has the social network. Twitter has the angry social network.”

To understand how we got here, it helps to look back to the early days. In 2008, after a user went public about her harassment and the service’s inability to stem it, Twitter executive Jason Goldman wrote: “What we believe is that Twitter is a recipient-driven utility; you choose what content appears in your timeline. We offer tools like block so that users can distance themselves from others with whom they have disputes or disagreements.” Which fits in with cofounder Ev Williams’s explanation of replies around the same time:

My followers will only see my update if they follow both of us (if they have their setting on the default).

We’re trying to avoid the situation of you hearing someone answer a question when you didn’t hear the question (for instance). Also, you don’t have to hear answers to the question from people you don’t want to hear from.

Dismissing the real harassment going on was bad, but the Twitter execs were right about how Twitter didn’t systematically amplify it. The underlying model for following meant that we all saw a slightly different Twitter, as I wrote in 2009:

The idea of Following means that the natural view we see on Twitter is different for each of us, and is of those we have chosen to hear from. In effect we each have our own view of the web, our own public that we see and we address. The subtlety is that the publics are semi-overlapping—not everyone we can see will hear us, as they don’t necessarily follow us, and they may not dip into the stream in time to catch the evanescent ripples in the flow that our remark started. However, as our view is of those we choose to follow, our emotional response is set by that, and we behave more civilly in return.

That we had to go to a little extra effort to see the replies then—they were in a separate tab, weren’t under posts, and were not sent as notifications—reinforced this cultural feedback loop. If you’ve read @AllTheTwits, the account that reposts tweets from 2007, you can tell how different the atmosphere was. The service had built a way to dampen anger and encourage discourse. Suw Charman-Anderson makes an architectural analogy to describe what she calls a valuable “privacy gradient”:

The idea of a privacy gradient comes from architecture and refers to the way that public, common spaces are located by the entrance to a building and as you progress through the building the spaces become more private until you reach the most private “inner sanctum.” . . . As one moves along a privacy gradient, one is also moving along a parallel trust gradient. As you invite me deeper into your house, so you are displaying increasing trust in me. . . . Six years ago, I thought that Twitter had a basic, but basically sufficient, privacy gradient. And, indeed, it might have been sufficient for the network in 2010, but it is now completely insufficient.

That might have seemed unintuitive given notions of the freewheeling, public web, but it made Twitter a productive medium for conversation.

If you accept Habermas’s assumption of a single common public sphere this makes no sense—surely everyone should see everything that anyone says as part of the discussion? No. This has never worked at scale, and elaborate systems ensured that only a few can speak, and only one person can speak at a time, because a speech-like, real-time discourse was the foundational assumption of debate.

The destabilizing changes came about when engagement was taken as a goal in itself.

This public worldview became the default assumption of communication online too. We see it now when privileged speakers decry the use of anonymity in the same tones as 19th-century politicians defended hustings in rotten boroughs instead of secret ballots. The tactics of shouting down debate in town halls show up as the baiting and trollery that made YouTube comments a byword for idiocy; when all must hear the words of one, the conversation often decays. First with blogs and then on Twitter another way emerged—many parallel overlapping conversations that spread ideas memetically rather than through Robert’s Rules.