Also if you are not hung-up about total “privacy”, “Unlisting” is a way of taking a Topic off the mainstream view and calming it down without it appearing for others in lists and digests (even though direct links will still be accessible by the same people).
It’s a bit like having a huddle in the corner with someone even though others can see the huddle if they are told where to look and can listen in if they really want to (but are unlikely to have their attention drawn to the huddle).
I believe staff can always see an Unlisted Topic in lists, and you can always re-List if you feel the issue is resolved sufficiently.