How much should game companies control what can be said in general chat?

In online games with a multitude of players, one great feature is to meet other people in an open discussion, talk about the game you are playing, and learn from one another. Many times, this can initially happen via the player-wide General chat (or whatever a certain game’s equivalent is). In World of Warcraft, there are other, more specific channels, like Trade and LookingForGroup, though these channels do not usually function solely for these purposes and have a lot of generalized chats as well.

This is an important — or maybe even a necessary — function of the game. That is one of the main reasons to play an MMO, to meet and converse with other people. There are ways to talk to people individually, of course; there are more private options such as being in a party or within a guild chat. And in many games, there are ways to ignore specific problem people. Chatting long enough will inevitably attract trolls who try to derail the conversation or intentionally inflame people. Ignoring the conversation at that time or temporarily leaving general chat is always a healthy option. However, this is in response to specific, negative trolling, that perhaps moderators could punish with warnings, suspensions, or even permanent banning.

What about topics that instantly spark controversy just by nature of being heated topics? In many chat channels, politics will often come up. Even without a troll involved, tempers usually flare. This is a game, though, and people are there to have fun — perhaps politics should be on a list of topics that shouldn’t be discussed? Certainly a different category but with similarly impassioned individuals — what about sports? Sometimes, smack talk can go too far when sports are involved. Keeping general chat to only talk about the game they’re in? Alliance/Horde smack talk will set off the profanity filter.

Should general chat be moderated? If so, how? Against trolls, against specific topics, limited to talk about the game? Could trade and LFG channels be used for their intended purposes?