I wonder what would happen if you had all the movie's participants were together in one theater to watch the movie and themselves in the movie -- and the aftermath.

A great idea! The art is not in the work, but in what happens when we see the work. And then not even in that, but in what happens, when we see, what happens when we see what happens etc...

a million competing religious ideas that can't all be right.

What do you mean by being right or wrong here? The ideas are just electric currents in the brain; these currents lead to emission of acoustic vibrations that are then translated back to electric currents in another brain and then stored in memory there, if the currents are in some kind of harmony with the other vibrations (bits of information) there.