Permitted viewer roles
Select which roles are able to view discussion topics. You can select multiple roles here (Administrators are always able to view topics)
If you would like everyone to be able to view topics, even users who are not logged in, leave this field empty, i.e. with no roles selected.
It won’t let me leave the field empty. How do I allow the public to view?
I figured it out by the response to somebody else's question.