Written rules aren't for the offenders, they're for the conflict-adverse community members who get uncomfortable when someone needs to be thrown out for community health reasons. They don't really have strong opinions supporting the person's behavior, but they're uncomfortable with the idea of people getting exiled from the community, so come slithering out to protest when an asshole is exiled for being an asshole. Since their primary reason for speaking up in the first place is discomfort with conflict, a quick "they broke the rules" tends defuse further argument.