@siloko:
For the same reasons that I reject a belief in a god, I will continue to choose to reject a belief of the nonexistence of free will until I am forced to believe in it (har har), on the simple idea that there is no reason for me to believe that I do not possess a free will that outweighs any reasons I have to believe that I do. This isn't saying "I just believe this but I don't know why." I believe it because the opposing argument has not made a case that is more convincing.