You have no idea the mental gymnastics zealots can get up to.
My grandmother was a fanatical roman catholic and she swore that all the stories about priests diddling little kids were a conspiracy by the rest of the world to discredit Catholicism.
I'll add that there's an element of denial and fear at losing community. For most ex-Christians I know, losing that familiar community is the last thing to go during their deconstruction. They might not believe in anything that's taught anymore, but leaving behind that community means isolation for a while and having to build new friendships and support systems.
So zealotry is definitely a component, but don't discount fear of being an outcast, either.