I would say github shouldn't even allow publicly visible code without a license.
> If you set your pages and repositories to be viewed publicly, you grant each User of GitHub a nonexclusive, worldwide license to use, display, and perform Your Content through the GitHub Service and to reproduce Your Content solely on GitHub as permitted through GitHub's functionality (for example, through forking).
> You grant us and our legal successors the right to store, parse, and display Your Content, and make incidental copies as necessary to render the Website and provide the Service.