Easy solution to see who's right:
Get a few Christians of different denominations, Jews and Muslims of different flavours to stand on top of a mountain in a rainstorm and get them to all simulateously blaspheme.
See who gets struck by lightning.
On a more serious note, I have to agree with Tormod that this is a pretty good post. However, in my opinion, I have issues with religious factions of all kinds trying to take exclusive ownership of morality.
In my opinion, morality is what drives civilization, and back in the old days, allegory and metaphysical explanations and presentations was more in tune with their understanding of the world, albeit a flat one at the time. Therefore, Moses bringing the Ten Commandments (there was fifteen, but he dropped the one slab

) down from the mountain, was just a set of rules and laws in a virtually ungoverned society. And, seeing as the "State" back then didn't have any teeth to enforce laws, a supernatural authority had to be linked to it to get the people to follow the laws. And it worked. People followed the laws, 'cause they knew they would pay for it after their deaths for eternity, or be rewarded for eternity. And that belief has propagated through the ages till today.
The reason that we still haven't given up on religion, in my opinion, is that religion resonates very well with ignorance. And whilst there are thousands of scientists having a fair idea how the universe works and being very skeptical about supernatural explanations, they still for a very small minority of the world's population. Ignorance is at the order of the day.
Maybe a proper test will be (although totally immoral and nobody except someone like Hitler would try it) would be to raise a community from babies to adults with no influence from outside and to see if they come up with a God-explanation by themselves, in other words, to see if the God-impulse exists naturally, or is enforced upon us by society, having had thousands of years of practice to refine their techniques.