Well that is a tough one. You would atleast need one public page for the guest users to see atleast sign in portlet for them to sign in. For rest of the pages, you have multiple options.
1) Just keep one guest page, this will be your home page with sign in portlet for guest users to login to your website. Dont keep any other public pages and just use private pages, whether they be community or organization or user.
2) Again keep one guest page for login. Now for all the other public pages, go to Manage Page of a particular public page. Click on permissions. Remove the View permission from Guest and keep view permission for Community and/or Organization Member.