I agree that it's impossible to prove God's existence, BUT there's a big difference between a believer saying, "I just saw a vision of Mary in the evening sky" and a nonbeliever saying, "I was in my study this evening and, well, I didn't see God around." Believers require no proof, and they can always insist that nonbelievers just haven't seen the light yet. True, it's a choice, but what if I said I had a bottle of magic WD-40 in my possession that cures blindess and speaks seven languages, but that I can't prove it because it stubbornly insists on working in mysterious ways. Would you then say that believing and disbelieving in the WD-40 are equally logical/illogical? As for the William James thing, check out Pascal's Wager. There's a wikipedia page on it that sets out some of the logical problems with that same supposition as James'.