IT isn't just Christianity being made fun of - it is the actual intended market that the producer was intending to make fun of. The whole movie makes fun of Christianity, southerners, white men, and generally every other thing that makes up the stereotypical NASCAR fan. Yet that is the exact target audience, and apparently that same group is eating it up.
Maybe some of the suggestions in the film about NASCAR fans is true....????
Or maybe the type of people who like NASCAR are able to laugh at themselves and their foibles.
That used to be considered a positive trait, before "being offended" became our national pastime.