Planetside had purity. There was no gear to farm from a boss. There were no pets or recipes to farm for. There were no quests to complete, money to get, no mounts. There was one thing to do. Capture bases. Maybe you could capture towers, or lay down defenses, or fly planes, etc. But it all was to one end. Capture bases. No one argued over what the game was about. No one ever logged in and said, "Sorry guys, I'm going to go farm gold instead of capture bases." If you didn't want to capture bases, you didn't log in. Now that's what I call purity of gaming.
World of Warcraft has none of this. If you want purity in WoW, you are going to have to build it, and enforce it. That means being a jerk to people. Who wants to log in to work on their Arena Team, only to be told that they should be farming mats for raiding or going on a raid to gear other people up? WoW isn't a game. It's like twenty games, and most of them are solo games. Many of them have requirements on how many people can participate. Impure!