This raises the question of what to do when you have inconclusive evidence. Should you follow the direction of the preponderance of evidence, even if you know that you are missing significant pieces to the puzzle? Should you remain without an opinion? Or should you choose whichever outcome you want, as long as it can somehow fit in with the evidence currently available?
Of course you should follow the preponderance of the evidence! How is that even a question? Obviously I'm aware that people choose to believe what they prefer to believe, but I didn't realize people were conscious of doing it, let alone rationalizing it explicitly. Kudos to Rabbi Student for being more self-aware and open about it than most, but really, how can you live like that?
Rabbi Student then shifts from Harry Potter's fictional dilemma to a real-life one faced by educated, open-minded Orthodox people everywhere:
Another area in which this dilemma arises is that of belief in theological principles. For example, the Divine authorship of the Pentateuch. Evidence from biblical criticism and related fields indicate that the Pentateuch was written by different people. However, an honest observer will admit that the evidence is not completely conclusive, and perhaps can never be when discussing the authorship of a text thousands of years old.
If the current preponderance of evidence points to human authorship, must we accept that conclusion? Or can we choose which position to believe, since either can somehow fit within all the evidence? Or should we retain the traditional belief of Divine authorship and dismiss new findings as either incorrect or explainable?
The message of Harry Potter is that there is no reliable method. Until we have all of the information, even the preponderance of evidence might be misleading. There might be some significant mising piece of information that will entirely change the picture.
Where does that leave us? Should we believe that vampires exist because they have not been conclusively proven to not exist? What about spontaneously generating lice? At what point do our beliefs become ridiculously irrational? What we have to say is that there comes a point, which cannot be objectively determined, when the evidence becomes overwhelming. We do not need 100% confirmation. At some point we have enough pieces of the puzzle that the conclusion is clear and we cannot ignore it.
Has the issue of human authorship of the Pentateuch reached a level of overwhelming evidence? I certainly don't think so, and I have written a number of posts on that subject. The message of Harry Potter is that when there is uncertainty then within the realm of rationally viable possibilities you are free to choose which to believe based on emotion (i.e. non-rational) reasons.
Now, as XGH points out, clearly you are "free" to choose what to believe in the sense that there's no rule out there requiring one to base beliefs on evidence. But if you make a pattern out of choosing beliefs contrary to the preponderance of evidence, the law of averages says that you're going to be wrong more than you're right.
Or, to put it another way, I'd love to play poker with Gil! Even when the preponderance of evidence tells him that he has the worst hand, he might just choose to believe the opposite and bet all his money -- after all "there might be some significant missing piece of information that will entirely change the picture!"