I have been in many rooms that are completely fine; technical rooms.
As for flagging problematic accounts: how would that work in a decentralized E2EE system, and do you think it cannot be abused? What would you want them to do if I flag your account a million times? Keep in mind they probably may not be able to keep up with it, nor do I expect them to. Additionally, you still should be able to use the service due to its decentralized, privacy-preserving nature, so the worst thing that may happen is getting banned from a Matrix instance, or a room.
Users tend to be less aware of these things than the operators of such servers (or at least, that's how it should be).
> Matrix is developing a privacy IM, you do not really moderate that now, do you?
No, but you can create mechanisms for the users to flag problematic accounts.
> Leave the rooms that raise your cortisol level.
The filth will follow the users. That's the whole game plan here: to cause grief.