According to triva (how sad is this)
"This was originally supposed to be a movie about people's ignorance of their own religion. When Steve Drain came across Fred Phelps he decided that Phelps had the most airtight theology of anyone he'd interviewed, and not only changed the course of the movie to focus entirely on Phelps, but he and his wife also joined Phelps's church/cult and made their daughters join as well."
Wow that is real sad. If I were Steve's wife, I would've grabbed those kids and left him!