Honestly not sure how I feel about this but there's a clear reason to be extra wary of false accusations here.
Because it's a private ring, there's no kind of transparency or accountability or oversight or anything, right? If you *are* falsely accused, you may never even know it's happened. There's likely no remedy possible. And I mean that beyond punishing the accusers or whatever, you won't be able to tell your side of the story or make a case that a story was wholly fabricated. And because the culture around this kind of thing is very strongly biased to believing accusers by design, it's hard to imagine even self-policing within the community.
Maybe the collateral damage and susceptibility to corruption are worth the benefit, but let's recognize there's obviously a trade-off here a "system" like this isn't downside-free.
If you never hear about it, it means it's not being widely spread publicly, so it will not affect your employment opportunities and so on. At most some women might keep their distance and not want to date you. If it's being spread publicly, that's when you have legal recourse for defamation.
But if someone really wants to tarnish your name and damage your reputation with a false accusation, would she really just bring you up in a private fb group? The false accusation is bad, but I don't see the private group as the problem specifically.