Well, the difficulty is that currently the moderators have no basis except gut feeling and our own perception of general sentiment on which to act. We don't have a mandate. There's nothing to say what merits a warning, when to ban someone, who should get an informal caution, etc.: we just have to play it by ear.
I wouldn't personally be in favour of a strict set of rules, either; that's why I use the word "guidelines". General principles of conduct are more what I would suggest: say, for example, being civil, operating through moderators rather than disrupting threads with accusations and arguments, that sort of thing. More like an agreement regarding due process than anything else. Rather than rules or guidelines, even, it could just be an explanation of how to report your concerns to the moderators, since most concerns we'd be able to handle on a case-by-case basis. Mostly, these would be the kind of things you'd just take for granted, but it's a lot clearer if they're written down rather than having to be assumed.