He attempts to instruct people in it at every reasonable opportunity (at least in the earlier parts of the story), and strongly indicates that his ideal world is one where everyone is "sane". In addition, we know that the fic's explicit purpose is to promote rationality to those who might otherwise not encounter the concept (specifically HP fans and fanfic readers in general), and that Harry is the author's primary mouthpiece to this end (though this is not to say that his own use of the methods of rationality is always successful).