If the details of moderation rules were public, companies would be facing additional labor costs dealing with posters pushing hard on the edges of those rules.

If the details of moderation rules were public, companies would be facing additional labor costs dealing with posters pushing hard on the edges of those rules. If the rules have really hard edges. I think that's very unlikely. I think the substantial reason companies won't publish their moderation rules is almost certainly that they don't have much more than a few bullet points - and a page of "things the lawyers have said you mustn't let people say" - and otherwise leave it up to the whim of the moderators. Having said that, it might well be illegal - or in contempt of court - to publish the list of things that are moderated for legal reasons.