Actually, it doesn't take a server FULL of griefers, only the majority of the server should be griefers for this kind of griefing to work.

Only give negative rep when the player is kicked / banned from a server.

So it takes a server full of griefers to give negative rep.

The idea of a Rep. system to counter griefers got me thinking; it would reduce the ability to grief in game by eliminating players, but couldn't this spawn a new type of griefer which purposefully gives people bad rep. in order to force people out of games? Or, if people are banned from AoS, (forgive me if this is wrong) couldn't griefers just create new emails & accounts, due to the openess of the registration system?