surely this is not unbiased...

I don't think I've ever seen such an unbiased documentary on crazy people. Take Jesus Camp for example. It seems like they played up the fact that they were crazy more (not that they needed the help). I thought this was quite unbiased. I was actually impressed that they let the Church's own insanity and complete lack of compassion for the fact that people have differing religions and lifestyles speak for itself.

Is there such a thing as an unbiased piece of art?

Whoever has the instinct to create something obviously has a response, or else they wouldn't be devoting time to it, and there's no way to totally sublimate that.

I would argue that it's completely unbiased. The documentarians pretty much just turned their cameras on and let the people do whatever it is they do. You only hear the voice of the director once. My biggest problem with the film was this it was TOO unbiased. The director doesn't take any kind of opinion on what he's filming or put it in a broader context. Yes, the behavior exhibited would be considered "absolutely insane." Certainly, I think the scene about 2/3 of the way in where we see the congregation pretty much throwing themselves into epileptic fits and screaming glossolalia sums it up. However, the people themselves are often portrayed very sympathetically and positively. It's clear that the truly crazy thing is their beliefs, not the people themselves.