If mod warnings are sent via PM, this would be fine. If modding is public, it’s a fail, because a warning is, by itself, far from upbeat!
I don’t believe, human nature being what it is, this could be sustainable. But I don’t object at all to the idea of the rule, and I applaud the motivation.
For a fan club — an organization devoted to celebrating some person, group, or thing — I guess it makes sense to demand positivity. You’re not going to get much depth of discussion, but that may be beside the point.
It’s primarily on FB and the mod will delete things without warning. It’s run by a woman who has been a “fan” of the thing for several decades and I have a feeling she’s the “Uber Mod”.