APPEAL TO CONSEQUENCES: SDB asks "Do you prefer unpleasant truths or pleasing falsehoods?" In almost every instance I believe it's better to know the truth than to believe in something false just because it's more comfortable. There are plenty of examples, particularly that relate to religion, but since I said "in almost every instance" let me briefly discuss one case in which the truth seems irrelevent.
Is there such a thing as "free will"? I believe there is -- if man is created in God's image, then the most significant implcation of that is our existence as free moral agents. It gets to the root of one of the biggest questions that many people have about God: if God is completely good and also all-powerful, why is there so much evil in the world? Because he gave us the ability to make choices, even choices that don't coincide with his desires. Free will is essential to Christianity, because without it there would be no value in talking about good or evil, both of which rely on intentionality. God imbued this physical bodies with a supernatural essence, a spirit if you will, that transcends the mere material universe.
From a scientific perspective, however, there isn't much explanation or allowance for free will; additionally every conceivable investigator is himself trapped within the phenomenon in question. How can I possibly determine whether my own thoughts and actions are the result of choice, or whether they are predetermined by chemistry and physics? My decision-making process is hopelessly and fundamentally tainted and depends entirely on the result being generated. This difficulty is what I call a "containment problem", because our reasoning itself relies on the answer we're trying to come up with.
Most of the non-Christians that I've asked believe that there is such a thing as free will (does SDB?), but none of them has a credible conjecture on the source or nature of it. If our intelligence is wholly dependent on the biology of our brains, then how can we be anything but complicated deterministic machines? Some have turned to quantum mechanics, but no one yet has an understanding of quantum effects that could be used to explain the origin of free will. Even if QM plays a significant role in the high-level operation of our brains (questionable), this just serves to introduce macroscopic randomness to the system... would they argue that this is the same as free will? If so, it's a different definition than I would use.
In the end, I don't think it matters. Although SDB wouldn't like it, an argument based on "appeal to consequences" appears to give the most satisfying answer possible. If there is no such thing as free will, then the question itself becomes rather pointless. If we're all just biological computers running complex, chaotic programs, then why even bother having the discussion? Acting as if we do have free will is the only practical option (how would you act otherwise?), and so we may as well believe it to be true.