alt Hacker NewsSure.
In practice, in federated networks bad actors end up being blacklisted. It does not provide any "formal" guarantee, but… it tends to work fine enough. For this specific "deletion request" feature, of course it should always be seen as a convenience thing, and absolutely not about security.
As with many engineering things, it's tradeoffs all the way down. For instant messaging, a federated approach, using open protocols, offers what I value most: decentralisation, hackability, autonomy, open source. My options in this space are Matrix or XMPP. I have not attempted to self-host a matrix server, but have been very happy with my [prosody](https://prosody.im/) instance for almost a decade now.
I don't know what's wrong with XMPP other than the network effect collapsed when the GMail chat thing was killed, while the mobile client options were poor for a very long time.
Matrix has the appearance of being a drop in replacement for Slack or Discord, but the design decisions seem so compromised that the only explanation is they did manage to establish a (somewhat weak) network effect? It certainly is not a good look for an open source project to be running on Slack or Discord (free/cheap plans rugpulled or to be soon.) Then that leaves IRC, which has a network effect collapsing at a much slower pace.
I never got far enough to try hosting a matrix server, but reading the linked post -- Matrix definitely is not GDPR compliant. The combination of whatever end form of ChatControl the EU gets along with possibly hundreds of other laws across the world and individual US states makes me think the days of a public facing non-profit or small startup running a project like this are over. (Or maybe the future of open source is funding lawyers while the development is all done for pennies by AI?)