I love this question. And while I think a "Pascal's Wager" approach is reproachable regarding notions of religious compliance, a parallel train of thought addresses this question rather cleverly.
If you believe we are determined, and you are right, then you believe it because you are determined to do so. However, if you are wrong, then you are choosing to believe in determinism.
On the other hand, if you believe we have free will and are right about it, then you are choosing to believe in it, whereas if you're wrong, you're determined to believe in it.
There's only one option where the answer you choose to believe is the right one. Therefore, if it's possible at all for free will to exist, it's preferable to believe that it does.
Keep in mind that I say "preferable" and not "rational." This argument appeals to human motive, not human reason (which admittedly, so does the original Pascals Wager, though to a more disastrous end).
If you believe we are determined, and you are right, then you believe it because you are determined to do so. However, if you are wrong, then you are choosing to believe in determinism.
On the other hand, if you believe we have free will and are right about it, then you are choosing to believe in it, whereas if you're wrong, you're determined to believe in it.
There's only one option where the answer you choose to believe is the right one. Therefore, if it's possible at all for free will to exist, it's preferable to believe that it does.
Keep in mind that I say "preferable" and not "rational." This argument appeals to human motive, not human reason (which admittedly, so does the original Pascals Wager, though to a more disastrous end).
