While we all have different preferences and game styles, I think the reason bay12 remains generally orderly and harmonious is because we simply are all equally insane deranged reasonable. Dwarf Fortress is obviously a game that takes significant amounts of patience, perseverance, logical reasoning and foresight to actually get to a point at which it becomes Fun or interesting. We know that our scarily bad graphics and interface scare people away, but think about the types of people they tend to be, or more, the type of people that aren't and do stick with the game, trying to understand it. That's us.
Minecraft makes a good example of this, it is (relatively) similar in concept to DF, but is much easier to play. Yes, it is immensely popular, but look at the community, it's mostly complete chaos and while there are pockets of civility, they are constantly targeted by destructive groups.
The fact that DF has an almost impenetrable learning cliff actually helps protect the game. All these disruptive people and trouble makers cannot climb it, and run away. When faced with this learning cliff, most run away, others futilely attempt to run at it, and bounce off. Only we true dwarves, bay12'ers, see to instead dig a tunnel through it and emerge the other side, covered in stone, debris and the blood of those who would not have made it so far.
I'm trying not to seem too egotistical here, but for the most part this probably is true. Not to say we're any better than the rest of the internet (infact the average sanity and value for human dwarven life here is concerningly low), we do tend to be the more maniacal reasonable types.
Sorry if I offended anyone by calling them "reasonable", I know many of you would probably not see yourselves that way and it is probably not the correct word, I respect your self acclaimed (and duely earned) insanity.