Cognetive bias cannot be so easily overcome with just one reasoning point. It's a cleanse of sorts, it must start with the individual allowing themselves to have doubt, until then there is no point, if the org says batman is real, and they all believe... you are stuck until they can reason #1, then you can begin to have a rational conversation.
For me being inside all my life it was just the bible that I questioned and began to feel the WT explanations were phoned in and everyone was just bobbing their heads in agreement. So first I came to see the bible as a book of fiction... then it all fell apart... notice the cult manipulation practices that are a model used by many in undue control situations, and voila.
I also began to realize my rational brain never fully accepted many things.
then I'd hear very spiritual people who were highly privileged and highly dotted after say reprehensible things, knocking on doors and wanting to see some nice person get their come come-upins at Armageddon just because they felt content with their religious ideas.
There is no one or ten things you can point out until someone breaks the barrier of deciding to use their retinal brain, some evidence or specifics might get them thinking, but if they aren't really to be rational cognitive dissonance will quickly clean house.