Thinking it was sad that he had to write it at all. Unfortunately, the term "mature" and "gamer" are terms not usually associated with each other. I don't say this out of hate, I say this out of experience. I'm a 40 year old gamer who has been around since day one of the Gaming Age. The garbage I've heard uttered in game chat and seen erupt on guild sites would make a prison inmate blush.
Matt writes this article out of his love for WoW, but the topic stretches across all game genres and can (and should) apply to any assembled mass of people (whether they're in a guild, a clique, a supergroup or just friends hanging out) in any game - massively or fragger.