I think there are pros and cons for everything really for me the only way to fully stop this and maintain team play as we all desire is to ban multi accounting totally. So one account per person or per IP address.
I know there are programs to block your IP address which would be a way around it however I think many people are sick of multi accounting so we could launch a reporting system to basically report anybody who is doing it in game. One account per person per server.
Might be quite a lot to manage for the game makers though especially at the start but once a few accounts have been kicked off a server or banned or whatever then the rest would fall into line quite quickly