Now, one can be obligated by reason, in a manner of speaking. If a teachers shows you a perfectly clear geometric proof, you are forced to accept it, so to speak--it's not a choice. But how can there be an a priori discussion about what you may or may not believe, which forces you to choose beliefs?
It leads to some interesting consequences for the more rationally-inclined believers--the kind of thing XGH used to mock.
A couple months ago, I sat with a number of people, a couple of whom were wholeheartedly relating miracles and magical incidents that supposedly surrounded one of the Gedolei Hador. (Frankly, I found the supposed miracles to be parlor room stuff, but I'll put that aside.) One other person present made all the right skeptical points: was there any independent verification? For those people who claimed they were healed by the rabbis prayers, do we know the total number of people who asked for healing prayers?
But then he stopped and said: "But on the other hand, Judaism has some tenets of our faith that might sound silly to an outsider, but we believe them. Are we supposed to believe these kind of things are possible as well?"
I thought, exactly. Once one has admitted the concept of religiously mandated beliefs to the picture, how can one scoff at crazier beliefs? As far as I can tell, minimizing which beliefs are mandated does not help: once this is an acceptable notion at all, why not take all midrashim literally, or believe modern rabbis have prophetic powers? Etc. The reason, it turns out, is because our hypothetical rationalist doesn't think those beliefs are actually mandated--not because the beliefs are silly.