One of the points that Aurynn Shaw makes is that federation hampers the addition of protocol features because new features have to be agreed upon by all participants in the federated network. This adds friction to the evolution of protocols, and results in the phenomenon wherein Slack runs halfway around the world while IRC is still putting on its shoes.

She also makes some excellent points about the social characteristics of federated networks. In a federated environment, each node sets their own policy, which meant there was no single point of responsibility for onboarding new users, setting standards of behavior, or filtering out trolling and harassment. Often, as on USENET and IRC, it is the user's own responsibility to filter out content and users they don't want to see -- and there was no authoritative source for new users to determine who/what should be filtered. Some USENET groups were moderated, and on IRC, channel ops can monitor and ban users for in-channel behavior, but if someone is harassing you in PRIVMSG there's often nothing you can do -- and channel bans can be circumvented and enforcement bots subverted fairly easily. And no one takes responsibility to communicate which instance of a federated network to join if they don't want to see particular kinds of content.

So federated networks quickly become cesspools of the worst forms of communication because they're optimized to promote all forms of communication -- "freedom of speech at all costs" as Aurynn says (and, as she points out, is actually a US-chauvinistic perspective on speech and runs contrary to the laws on speech even in most democratic countries -- hate speech being an offense is the norm). This tends to make them grognard-friendly, but hostile to new users and to users of marginalized communities, as well as potentially illegal to participate in in countries not called the USA. And that was accepted in the 90s internet because that's how the 90s internet was. But standards have changed and this is no longer acceptable. "Me too" has gone from the mark of a clueless n00b to a rallying cry against harassment. And people like Aurynn Shaw and Coraline Ada Ehmke have been leading the way in terms of calling out and removing the negativity, exclusion, and sometimes outright hate, from open source development communities with things like Coraline's code of conduct and Aurynn's efforts to highlight contempt culture -- the "PHP sucks" and "Micro$oft sucks" culture that prevailed in technical circles in the 90s and early 00s whose toxicity is something we still deal with today.

Times have changed since federation came out and was promoted as a wonderful thing. Back in the 90s, we thought that building the technology itself was sufficient to change the world for the better. Today we understand better the social costs that mentality has unleashed. We optimize for creating safe, welcoming communities and promoting voices that are usually silenced, rather than allowing everyone to communicate anything at any time. Unfortunately, federated technologies as we understand them today still come from that 90s mentality, and without broader conversations about the social impacts -- as well as establishing some sort of standards for mitigating those impacts -- it's simply better to not federate. Slack and Discord are easier to get started with, offer more features, and promote a safer and more welcoming environment than does IRC.