MMOs are virtual societies and thus should emulate all the fun things we enjoy about society. It's as simple as that.
There needs to be enough order that people know the risks with breaking order. There need to be enough rewards for breaking order so that players break order.
EVE doesn't have an "unshiftable power structure" - EVE has had alliances come and go, some as large as 50%+ of the galaxy defeated by small knit bands of dedicated players. The game is too numbers-heavy, too 'slow-paced' for the average 'gamer' and this is obvious by how successful WoW is. WoW is successful because of base psychology - idiots see the yellow ! and do the thing until it's 10/10 then they see the ? and get all excited and get the thing and the gold form the guy then rinse repeat until max level where instead a few people in vent tell you how to dance for a few hours in order to perhaps maybe if nobody else wants it receive some thing with instructible values and PURPLE text.
It's about colors, instant gratification, shaping, modeling, skinner box stuff; mixed with a little peer pressure and dripfeed novelty.
I've played a few sandbox MMOs and more esoteric muds. These games are about exploration, character advancement, and character interaction lastly. Explore the options the game provides - viscerally or in terms of the options presented, then advance your character by finding things or doing tasks for others; lastly, you build relationships with people, be they friendships or rivalries.
One particular MUD I played, I played as a thief. A jerk guild was preying on new players and they were pretty careless about security. I lockpicked into their guild HQ and invited my whole guild inside. We made off with everything they had stored there and returned a lot of stolen items to the new players that were still sticking around. It was great fun and pretty exciting, you know, to break into a palce like that with your own wits and then impromptuly organize your guild to haul text-objects out of a text-room. This is something we'd never see in any mainstream MMO, because you can't have theft in a game that's supposed to appeal to the masses. You can't have anything that could be construed by "hardcore" by anybody. You need safety -- everywhere, almost all the time. Items and worlds and players need to be static, otherwise people might get upset. The most players will put up with is ganking and that's because they know all they're losing is a little bit of their time - and time isn't that important to these people yet.
There's a big difference between a good MMO and a successful one. You can maybe have both if you keep player populations small and tightly-knit, because then everybody knows your name- and it's less about how well you do in the game. But once you emphasize faceless raiding or loot hoarding players just see greed, envy, despair and desire- and taking away items, letting the game ebb and flow? That's too scary for them.