Curious; when I read Professor Quirrel going into "protect the information from Harry Potter" mode for Macgonnagle, I almost immediately thought this was deeper than "I've changed my mind and it is no longer a good day and holyshit he's going to kill us". The overwhelming majority of readers assume he is being sincerely cautious in an effort to save the universe. I was assuming that there was obviously a slightly deeper plot involved, though I hadn't gotten far in thinking about what before I read the suggestions about alternative sources such as the Chamber of Secrets.

(Harry's lecture to Macgonnagle on identity-based strategy actually made me realize something about myself I feel is worth analysis... somewhere. I may or may not get back on that if I figure out if it's worth publishing.)