A dev can't ban anyone from going online. The server hoster can use a whitelist, blacklist or a password protected server.
A quote from the gitter chat: "There will be a central authentication server to prevent impersonation. Server owners will be able to decide whether they want to use it for their server or not. (I.e. the old system will remain available for server owners to use if they wish.)"
In other words, in the future this will be able to be fought against, but at the moment noone except for the server hoster can ban, kick or do anything against trollers and/or impersonators...
I'm not saying you can't post this topic here. I'm just saying that you won't get any result from it since we can't do much about this. I'm going to allow the topic for now, but I'm going to keep a close eye on it. If it gets all drama-y again like some topics in the past, I'll close/delete it without a warning... (consider this your warning)