To a fundamentalist, the letter of the law is far more important than the spirit. As was the case with the pharisees, they are more interested in instituting codes of behavior than in encouraging a relationship with the divine. Such thinking is convenient, for it creates a point system that we can easily reference to know how good we are doing. But it is ultimately an insult to God because it tells him that his sacrifice was not enough but we can earn our own salvation.

It's hard to fight against that world view. I've seen nothing short of a personal experience with the divine change such people, and in the case of the pharisees, even that didn't help.