Facebook lets you add raw email addresses to conversations even if they're not registered with Facebook accounts.
As far as I can tell, there's no way…
…for the person who owns the email address to remove themself from the conversation (there's no unsubscribe link, replying with "unsubscribe" or "remove me" don't do the trick either).
…for the conversation starter to remove the email address from the conversation.
What am I missing?