Chartered Guilds are OOC. They are so OOC that they don't even *exist* within their Guild's Continuity. There's an old saying amongst roleplayers, that "In Character Actions should yield In Character Consequences." (ICA=ICC). Unless specified otherwise by their Charter, a Guild should only interfere in Roleplaying events if their Continuity is endangered. Within a Chartered Guild, other OOC groups can exist, but IC organizations must be validated by the Continuity.

IC Evil
A Guild may wish to specify that "evil" plots and "dark" organizations need to be cleared with the Guild first. A Guild can also forbid players to play evil characters, or reserve these as alts for those who have proven that they can handle it. Many online RPG's run on a model of "OOCly licensed evil." This Guild style of play can make it easier for a Guild to judge behavior, and the excuse of "It wasn't me, it was my character," is more clear.

A Guild can keep control of the Continuity by controlling the actions of the most ICly powerful characters who might not even be played by any player. A Guild can decide that it's winter, that there is a plague, that magic no longer works, that all characters using the Rodent character-shape are now skeletons. The Guild's power is naturally limited by whether or not players will remain members or leave to spend more time on something they like better.