Why is the chat system so abused?

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To everyone who plays wow, Isn't it anooying when people scam chat like theirs no tomorrow? Everytime I play I aware there's like a contest to see who can post the most in the chatbox. It's always about the most randomest stuff, and don't even get me started when someone bring's up chuck norris. Why does blizzard allow this? I think there should be someone watching the chat, that way we could get rid of some of the players that live in the chatbox. Now I'm not talking bout the players that play wow and are trying to trade, talk , get guides etc. I'm talking aboutbtjpse who just post tell someone comments and than scams them like they have nothing better to do. Why do you think this is? Is it for fun or are they just trying to be annoying? What do you think?