When there are only unwritten rules, then people trying to circumvent them will, usually and to my experience, get caught and stopped by the moderation. The lack of written rules usually means they have leeway in what they do so they can easily plug holes.

On the other hand, with written rules it's also harder for moderation to abuse their rights.

Either way, there will always be this commitment, the community usually figures out what they need by themselves when the decision becomes necessary.