I guess one thing that is important to see is that the theists almost always have a 'light' inside that is part of the faith-thing and its put there by parents at young age,cozy with mum and dad and JESUS! Its a terrible thing, 'be a god boy/girl or...'. But comforted at the same time thru genuin love by the same parents -you know "there wont be no santa if you dont..." But on existensiell level (why are we lying the santa thing by the way?-lie to kidz?)...Its a diffucult (cult hi hi) stone to move cause
its is emotionel deep and COULD be important for the person to keep it all together. Therefore the anger when touched....The concept 'barnatro' -child-faith - is known here in Scandinavia.
I think one positive way to do this is to pick apart at the little things that will be seen as challenges to their understanding of their faith rather than an attack on the faith itself.
For example, it is very possible to remain a Christian while dropping belief in an inerrant Scripture that has no contradictions. Make the case that a Bible with errors and contradictions reveals the flaws in man. Concede that it proves nothing about flaws in God. It just means man, in recording "the Word of God," did an imperfect job. Even the most ardent Christian has to admit the possibility. Then show him things that simply can't be explained away no matter how hard you try: The census at the beginning of Luke did not take place during the reign of Herod, for example. That's an indisputable fact that is impossible to reconcile with Scripture. It would be like me saying I was born during the Eisenhower Administration but before the end of World War II. Something MUST have gone wrong when the Bible was being written for that kind of dunderheaded mistake to have been made. It's not God's fault. It's the fault of the men who transcribed it.
Give that time to sink in. As much time as it needs. It will be argued with. It will be resisted. But in the end, it can't be disputed.
And once you have a Bible that CAN have errors and contradictions, then it becomes the responsibility of the reader to examine it a little more critically.
What happened to me was, I turned my attention to the book of Job, and I tried to see it from the perspective of everyone in the story BUT Job. You know, like his kids, who got KILLED because God wanted to win a bet with Satan. Holy Crap! How was that just? And then, in the end, to make it up to Job, got gets him new kids. WHAT?!?!?! That doesn't even work with kids and puppies! But God wants you to think that makes it all better? Only in a fairy tale is such an outcome even remotely "happily ever after." A reasonable person, upon realizing this, will recognize Job as a story, not a history. The implications of Job being an actual history would be distasteful when presented as a real thing that happened to a real human being. At some point, to protect the integrity of God, they HAVE to concede this story cannot be literal history and still be proclaiming a just God.
Now you have an errant, contradictory Bible that has fables in it.
Those two steps alone can take days, weeks or even a couple of years. But if they're being honest with themselves, they are inevitable.