rationalskepticism.org

It's tough to say how to deconvert a christian; more often than not, they won't give you the benefit of being there to see it happen. Someone who isn't genuinely interested in reality will have more to gain from saving face than admitting to having been wrong or inconsistent in their worldview. (And someone who is genuinely interested in reality will probably already have been deconverted.) As such, deconversions, in my experience, occur more frequently on private reflection long after I'm gone. What I've noticed works best, however, has more to do with emotional appeals than with objective evidence. Literally a hundred percent of the cases where I've met theists, known them as theists, and later again as atheists (~10 so far), their reflection always began for emotional reasons, and then they find that rationalizing their newfound position is far too consistent for them to be able to go back. In order for that to happen, they need both the emotional and the logical reasons as to why they should deconvert. Without the emotional reasons, they won't be roped out, and without the logical reasons, they won't find the consistency that keeps them out.

We've already monopolized on logical reasons, but what consistutes an emotional reason to leave christianity? You might be surprised! The key question to ask yourself is, what do they have to gain from deconverting? Avoid answering with things they wouldn't understand, such as cognitive consonance or guilt-free orgasms. You're more likely to win them over using simple desires, desires that anyone could understand, such as the attention of a nonchristian boy or girl that they like, or to avoid being laughed at by peers whose opinions they respect.

Hope that helps!

-Quip