Tongue firmly in cheek, Tobold asks what game companies could do to build a better community.
I'll take the question seriously and give several possibilities. But I'd also like to take a step back, and consider the greater strategy behind each idea. As well, remember that all things have a price, but some prices are worth paying.
A. Improve the environment
The idea behind the Broken Windows Theory is that "humans constantly monitor other people and their environment in order to determine what the correct norms for the given situation are." An environment in disrepair encourages people to be more anti-social, while a maintained environment prevents further vandalism.
Basically, the theory states that paying attention to small violations of social norms helps prevent larger violations. Accordingly, here are a couple of suggestions following this theory:
1. Have a strict naming policy
Normally, naming rules are very relaxed, save on Role-Playing servers. Enforcing stricter naming rules for characters, guilds, and PvP names would send a signal about what is acceptable and not acceptable. We've all seen the terrible, scatological, rude, and quite frankly stupid names that abound in WoW.
They're kind of like graffiti and petty vandalism. Making sure that names are decent (and also don't use special characters) might improve the general environment.
2. Stricter forum moderation
Hyper-aggressive forum moderation would set a the standard for what is acceptable behavior. Forum bans should also result in in-game bans, further linking the idea that how one behaves on a forum should match how you behave in-game.
B. Filter your audience
There's an old saying that "one rotten apple spoils the bunch." Here, the idea is that a single malicious player can destroy the community for numerous other players. That player might also influence other players to behave badly as well. Identifying and getting rid of that player might have the greatest impact on the quality of your community.
3. Be more willing to ban players
If it looks like a player is a bad influence, ban them. Even if it is debatable, maybe it is better to lose a good player than keep a bad player.
4. No PvP
If you follow the Bartle archetypes of Killer, Achiever, Socializer, and Explorer, Killers are the ones who enjoy harming the game experience of others. Killers are also greatly attracted to PvP. Getting rid of PvP gets rid of a major attraction for those players and makes it less likely that they will join your game.
There's some circumstantial evidence for this. First, battlegrounds have always been much worse than dungeons. Heck, I've been in BGs that featured vicious insults and trash talk when we were winning!
Second, of the MMOs I've played, the Lord of the Rings Online community (at least prior to going F2P) always had a very good community. I don't think it's a coincidence that it's the one game that featured the least PvP.
C. Remove sources of conflict
Maybe to improve the community, the best thing to do would be to remove the things players fight over.
5. Make the game easy.
In my experience, players are pretty easy-going as long as they are successful. It's really only when failure happens that the knives come out. If the game was much easier than it is, maybe players would have less to fight about.
Anyways, those are some ideas to improve the community of an MMO. Remember that they all have drawbacks, which I really haven't discussed at all.