I wouldn’t care if other instances just blocked them outright. It would suck for those who are registered there, but to me, it’s no different from defederating from Nazi apologists.
Based on this, I would almost suggest creating a third "Fediverse" community, be it on lemm.ee, sh.itjust.works or reddthat.com, communities known for honest admins, and with a group of mods that could be trusted.
However, I guess finding people wanting to mod that kind of place would be very difficult based on this kind of threads.