This sounds more like a paper topic than a blog entry, but here goes...
I think that this is obviously more of a complicated issue than usually given credit. Rules are definitely made for some sort of reason. When we're talking about gaming environments, rules are generally made to keep the gameplay fun, for all parties invovled, and/or to keep to a certain storyline or objective that a game is trying to accomplish. In MMOs, the "rules" are what generally keep the masses satisfied with gameplay, and help the developers to provide as much fun as possible to their consumers for as long as possible while keeping everyone on the same playing field in terms of capability in the game.
In the real world, rules are are also complicated. In the real world, rules are made for a variety of different reasons. For the safety of the general public, for the common good, to protect the poor, to protect the wealthy, to maintain intellectual property rights, to maintain physical property rights, to keep the powerful in power; these are all reasons that rules, or "laws" as we call them in the real world, are enacted and upheld.
So, to the point of the question: is it every justifiable to break these rules that are set before us. While rules are definitely subject to the choice of those they are set before to either follow or stray away from, I believe that in general, rules should be obeyed. Without any type of common rules that populations in general may follow, certain chaos is to ensue. However, at the same time, rules are generally dead-ends, they are the expression of some sort of subjective ideal that drove the law to first come in to existence. In this regard, rules should not always be followed, for if they were, then nothing would change. Two words come to mind: civil disobediance. Without rule-breaking, the civil rights movement would not have had impact. Yes, they broke the rules, but peacefully, and for a higher ideallic notion of equality for anyone and everyone, not just a certain race, not just a certain color. Rule-breaking in MMO games, however, might be a slightly different story. Since the rules that are in MMO games (at least to my knowledge) are the result of game designers trying their damndest to create an equal playing field of enjoyable experience for all players equally, I think that it is very hard to justifiably break the rules set forth by these games. Bottom line, especially in MMOs, it is my opinion that rules set out by game designers should be followed. However, if there are situations in which rules are in place that are disagreeable by a majority of the population, and do not significantly affect elements of the game such as equality and fairness for everyone involved, action should be taken to some way correct the shortcoming of the game, even if it means breaking a rule or two to get the point across. The important thing is to keep in mind that every rule you break has a consequence, intended or not, and those consequences need to be properly evaluated before taking action.