Ok, this is going to be long, so feel free to skip it.
The thing is, what I like about GW2 is that the developers have the same I deas as I have about how MMOs work. Traditionally MMOs have been at heart single player games with forced multiplayer. The default option until now is that everyone is an enemy: either literally if he's of the opposite faction, or simply because by being there he can "steal" your reasources and kill the mobs you also needed for your quest. Of course, you can group, but now we're talking about an extra effort, however small - unless you take the time to setup that group, everyone is an enemy or a competitor.
Multiplayer content has its own logistical problems; the fixed amount of people in a raid, the rather strict composition, loot drama, rotations to be kept in and out of the raid, and so on. Now that I think on it, if I wanted to make sure nobody was going to do raids I would have done exactly that. It comes, really, from the earlier days of MMOs where content was scarce, players were absolutely dedicated and you had to make sure content lasted as much as possible by putting as many obstacles in the way as possible.
So, traditional MMOs actually, paradoxically, reward solo playing with more actual playing time (I don't count the time spent spamming chat channels with "LF tanks instance X and go" and when I got the tank another half an hour "LF healer Instance X and go" because the healer had to go when the tank arrived as playing) and less dealing with idiots. To me, the solution was evident; set up the game so the default state of players is cooperation, not confrontation. set up multiplayer content so an specific combo and number of players isn't needed.
So far GW2 seems to be doing that quite well.