In a single player RPG something like a good and evil system works great, however it couldn't really work well in an MMO because obviously different players make different choices and you can't effect the in-game world in conflicting ways at the same time. I guess a system of good and evil could be implemented but it'd never really be to the extent that you'd like, it'd only be minor storyline changes. If you really want a chance to effect the in-game world Runescape isn't exactly the game to do it in.