Very much like Christians, who view atheism, or even other religions as a repudiation of their own. The true believer is all too aware of the conflict between their nonsense and the real world, hence the cognitive dissonance. They are already so insecure that they (think they) need their beliefs as a crutch. Knock that crutch out and they collapse. That is always happening to some degree, and their whole personality distorts until anger and hatred replace anything constructive.