I'd much rather like see people/projects running their own irc/xmpp/matrix under their own domain so that this situation can never happen again to them.
The moderation workload providing a public platform, especially one that allows direct peer to peer communication, is intense. Spammers, trolls, 1337 h4xx0r scriptkiddies and other "for the lulz" types on one side - these make a ton of work as they're openly visible, diminish the value of the platform and are not shy of using some 10$ a hour rented botnet to essentially kick you off the Internet... and on the other side, criminals that want to fly "under the radar" for you and expose you as platform ops to some serious legal risk: child abuse and warez.
There's a reason why there aren't many IRC servers/networks left over... it's incredibly expensive and taxing to run them, with users leaving en masse towards closed-source walls like Discord and Slack (which both have brazenly copied IRC principles!).
Thanks for the write-up, however... there is one thing that pops out: assuming there will be externals, be it antifa, NCMEC or a government, who provide feeds of entity IDs associated with Nazis, child abuse, stalking, doxxing or pirated content - would not such a feed be an immediate confirmation "this is the real deal" for those actively willing to search for such content?
"Not wanting to play god" is an admirable position, but there are classes of content where staying somewhat neutral-ish is dangerous as hell.
Those are all important points, though I wonder: with registration required, tied to email accounts, and if we were all running thousands of small irc/xmpp/matrix servers instead of one big system that is indeed simple to attack, would the dangers still be that serious?
Well... if you're the person that the server, domain name or association leadership is legally associated with, you are the person where the feds will knock on the door and raid if someone uses your server for pedo or warez content.
A bigger entity like a foundation, corporation or university (hopefully) has financial resources to pay for lawyers, to institute compliance and screening procedures and other things, but average Joe Admin does not. This is something many German TOR operators had to discover the hard way - especially dealing with the stigma of cops showing up for a CP investigation...