I love the mind of a typical programmer/designer/engineer. They are so used to dealing with logical programs and mechanical systems that they are deluded into believing that any problem can be fixed, patched, or worked around. This usually works for most things, but when it comes to human nature, these are temporary measures at best.
Too often in game design discussions (particularly MMO discussions) people reach the conclusion that the main "problem" is some trait or another that people exhibit in game, whether its greed, sadism, selfishness or just the mindless pursuit of awards and power. The designers view these traits as problems to be solved or worked around using game features that simply preclude the players from indulging in this behavior. The perfect example is friendly fire in your own faction. In WoW a Horde player can't walk up to a Horde NPC or another Horde player and attack them. If this were allowed it would obviously give rise to massive player killing and an irritating plague of griefers in starting areas and cities, so immersion be damned, we're changing the rules of reality.
The same goes for Gold Farmers, Twinks, Loot Ninjas, Channel Spammers, and every other type of MMO degenerate. They are the result of a genuine human need for money, attention, and power. On the other hand, so are Hardcore Raiders, Powerlevelers, Arena Champs, Guildmasters, and basically anyone at level cap. The very needs that lead a minority to become MMO scum are the same needs that drive the majority of players to play and stay in the game. Therefore, any limitations to the pursuit of those needs will affect all players negatively. But that is the method of choice it seems.
Instead of viewing these flaws in Human Nature as obstacles to be avoided or overcome, why not face the fact that these unflattering characteristics are a part of every person's being, and since its been that way for thousands of years, we are not going to miraculously cure it with the next weekly patch. Why not embrace these traits and allow them to drive additional hours of entertainment for players?
Tired of player killers? Set them loose on each other with something like a Bounty Hunter job system. Kill a player? Their faction automatically puts a bounty on your head, which players with the Bounty Hunter profession can pursue by either offing you or capturing you for more money. Kill a lower level character and your bounty goes up exponentially. Player Killers would flock to this profession and regulate each other. Oh, and if you're captured instead of killed? Time in a public prison where you must spend a set amount of time (logged on) in the stocks, where free players can taunt you. You'll think twice about camping the new player villages. Oh and players and guilds with money can set their own bounties on other players, so if someone ninjas one of your guildmates, you better believe they need to watch their backs for that bounty hunter you sic on them.
Don't like Twinks? Well thats your fault for having levels in your game, but thats a discussion for another day. If a guy wants to dominate in low level PvP and uses ridiculously OP'ed gear to do so, he should have the right, but with great power comes yada yada yada. Assign the highest gearscored 15% of players on each side of a PvP instance/zone the rank of Leader, General, Commander, Squad Leader, Chief Corpse Teabagger, whatever you want to call it, and give them special group abilities like setting visual waypoints, drawing on the map, and chatting specific groups on the fly. Also give them the opportunity to earn more honor/reknown/points. The tradeoff? They're flagged as leaders to your opponents, and are worth super duper extra points for killing. Hope your gear is good enough now!
Gold Farmers are not a problem in and of themselves, but they do encourage two different bad meta-behaviors: Account Theft and Gold Buying. Both of these can be easily addressed by having the company that runs the game offer to sell gold to players. I can hear the wail of the Anti-RMT Police sirens coming to get me, but before they do, think about two guys standing in a capital city decked out in identical epic gear. If one knew that the other had bought his gear with RMT gold instead of grinding countless hours and dungeons to collect the set piece by piece, he would feel discouraged, outraged, and cheated. But who is going to admit that their gear is bought? Gold buying would still be the dirty little secret of MMOs, it would just be legal now. No matter how much you argue that gold buying is a heinous crime fitting for only the lowest and least skilled of noobs, some people are always going to want to take a shortcut, even if its illegal and indirectly results in another player being victimized. Just roll with it and mitigate damage to other players.
I hate that we humans are plagued with deep seeded greed, laziness, selfishness and power cravings. I wish we could somehow help everyone overcome these defects and form a more perfect society. But we can't, not even in an MMO. What we can do is harness the motivational force of these desires and use it to provide even more entertainment and balance for our players.