I like the idea for whitelist, but I think for the survival of the server it should stay public. We don't have an effective way to get and keep players, we rely on the public part of the server along with public cop to keep the server active with players.
Huge servers you may watch streamers play depend on content creators for their player base and to keep it alive, which we don't have.
I think a stronger alternative would be requiring players to;
1. Join the discord server
2. Type a command in #commands such as -verify
This method would allow the majority of players who are here to roleplay to join and deter the rulebreakers or trolls away.
This would also be very similar to tokovoip, players who didn't want to go through the steps of joining the tokovoip server usually were trolls and didn't come to actually roleplay. Tokovoip is now obsolete compared to mumble, but having a verify command would definitely give us that sense of whitelist, but still allow new players to come and enjoy the server.