One of the best things about WoW is also one of the worst things. I'm talking about instances. It's great to be able to go on a adventure with your guild without being disrupted by others or have to wait in line to kill a boss. But having soo many instances in WoW also have a negative impact on the community itself. It's no longer possible to go into a dungeon alone and just spontaneously group together with the people you'll find there, and no, meetings stones isn't a working solution for this.
This means that people who don't have enough people in their guilds will be forced to stand in the middle of the major cities and spam "Looking for group/more/priest" in a hour or two, just to be able to enter the dungeon. This is both time consuming and defiles the other so important chat channels with spam and ruins the community feeling in-game. Also big guilds tend to become very elitish because of this, and refuses to cooperative with other guilds and players.
Blizzard constantly releases more and more instances into the game, so the effect will be more and more appearant with each new introduction of a instance. In no way is a instance needed for every little dungeon in the game.