While the existence of an All Members group is a very useful feature, it can cause issues when it is carelessly used or if Collection Owners aren’t well-informed about who may be part of one’s Guru instance. It would be valuable if Guru Admins have control over whether or not this permission group is available as an option to Collection Owners.
In the meantime, our workaround is to educate Collections Owners about the potential implications of using this permissions group and we’re creating larger permissions groups that they can use instead.