Communities can wall themselves off and be very selective in who they let in. That's not the problem. Block-prevents-replies allows bad actors to unilaterally

Communities can wall themselves off and be very selective in who they let in. That's not the problem. Block-prevents-replies allows bad actors to unilaterally silence opposition so that nobody else can see what the opposition's arguments are. *In a community that appears to be public.* daenz's system is interesting (anyone can ban anyone, but to ban them you must reply to the comment you're banning them for, and others can ban you in return), and it might converge to stability, but each new troll will disrupt some discussions until they lose interest in being repeatedly counter-banned. I think any system to exclude bad actors and prevent brigading needs to be designed some other way, so that silencing dissenters requires some consensus and can't be done unilaterally or by a small cabal.