Jesus Camp! That film terrified me because it depicted the same spiritual scene I grew up with as a teenager - uber spiritual shaking and tears and oobla doobla praying, the whole intense package ... except the film's version was centered around kids
. Put an entirely different spin on the Holy Spirit and my perceptions about what is genuine.
But perhaps the scariest part of all was that home schooling scene where the kid was being taught that global warming is false because evolution is false.