-1 This isn't as big of an issue as it seems. Minges come on to the server, they MRDM, you respawn and go back to what you were doing. If it hurt RP in that instance then take a deep breath, ignore what happened and resume the scenario or even reset. The Minge gets arrested, kicked or banned and we move on with it. The current system allows players and staff to focus more on playing that game itself then spending 15-20 minutes (with a good CC not a minge) "training" them.
In the instance where you mention someone was perma-banned and were still playing, shouldn't this situation have been escalated to +D (if it wasn't that is)? If they are using Alt accounts isn't that a greater issue here then the training system? If it is 100% confirmed they are an ALT that is.
Going to use my soapbox here and say that, what @Bacta is saying in terms of interacting with CTs for their first impression is incredibly important, but isn't necessarily a thing only staff should do but as a community. Give CTs a chance and treat them like they are already in your battalion, help them out, don't just make assumptions. If treat new players with respect and as equals they may stay around, Minges may reform, but if you are just being a dick to them, they will always remain a dick.