I’m here to tell you about my favorite Matrix feature that nobody knows about: Federated auto-updating blocklist sharing.

If you decide you trust somebody else’s decisions, at some other organization – their judgment calls about who is and is not welcome there – those decisions can be immediately and automatically reflected in your own. When a site you trust drops the hammer on some bad actor that ban can be adopted almost immediately by your site and your community as well. You don’t have to have ever seen that person or have whatever got them banned hit you in the eyes. You don’t even need to know they exist. All you need to do is decide you trust that other site judgment and magically someone persona non grata on their site is precisely that [non] grata on yours [too].

Another way to say that is: among people or communities who trust each other in these decisions, an act of self-defense becomes, seamlessly and invisibly, an act of collective defense. No more everyone needing to fight their own fights alone forever, no more getting isolated and picked off one at a time, weakest first; shields-up means shields-up for everyone. Effective, practical defensive solidarity; it’s the most important new idea I’ve seen in social software in years. Every federated system out should build out their own version, and it’s very clear to me, at least, that is going to be the table stakes of a federated future very soon.