Hi Marc,
Thanks for the input. Yes, content can be copied, screen shots taken, but that takes more effort and there is always a level of plausible deniability (that the content was faked). That's not case if others can view the original content for themselves. Further, for the person who nefariously invites in someone to the conversation they should not, they can plausibility claim no nefarious intention.
Yes, I can limit conversations to just two members, but that's a rather restrictive thing to do. I do not believe I have come across another messaging system which behaves this way. Or maybe I don't get out enough.
Does anyone know of an add-on or code to change this behaviour? I suppose the simplest thing to do would be to disable the ability to add in others to an existing conversation.