Right now we use a ZMI to delete content. It works, but is not elegant. When trying to delete a category with content, nothing happens. It should give an error message saying, "You cannot delete a category with content. You have to first move the content elsewhere, or delete the content."
Similarly you cannot delete a private category, whose group part has content. It needs an error message.
Eventually there should be a delete menu option. Try an illegal delete the GUI gives a clear warning. There is delete private delete public and delete both.
The warning messages are criticla, the rest can wait.