Aww, let ’em, I say. Girls just wanna have fun.
We cannot regulate people’s behaviour in private, despite what Gillian Triggs might want to do. If people want to do and say toxic things, then they are free to do so (unless they are planning terrorism or other violent crimes.)
If people say things in private, then they are owed privacy. If those things are said where it is believed they are private, then no public disclosure should have any negative impact on those people who said things in private. They are private conversations and others who were excluded from the conversation and have no rights to being privy to them.
It’s like police evidence collected illegally; it is inadmissible and for very good reasons. You have no rights to that evidence or conversation.
This applies whether it is a closed facebook girls group or US politicians.
If you are committing a crime though, well… that’s different. But the collection of material still needs to be collected IAW the law.