Comment by ctrlp

A stupid simple way to do it would be to use control groups as security pools. If you are not a member some master control group, then you can't be added to related spawned "child" groups. Better than what is there now, which is nothing. Would have to be client level controls, maybe a smart contract could govern, but could Signal build on the current abstractions by having groups be members of groups and inherit the same "phonebook" as the group they are a member of. Just spitballing.