I grew up in a family of believers, but we weren’t heavily religious, we didn’t regularly go to church. What changed my mind was actually debate.org. Although I was a believer, I didn’t really participate in religious debates. It was just a thing I believed but never really questioned why.
Then I came across a debate that blew the hole wide open. The debater made the argument that if any person deserved to go to hell, it would have to be God himself, because he is ultimately responsible for the suffering caused in hell.
This debate made me realize that I knew deep down inside religious ideas were silly, but what kept me from questioning them (which is why I avoided the religious forum) was the fear religion installed in me to never question God. Once I realized what it was that was keeping me from applying the same critical thinking towards religion as I did towards everything else in life, that disappeared.
And here I'd always said that online debate was primarily recreational and never really changed anyone's minds. I guess you never really can tell. Maybe it doesn't change minds so much as catalyze a reaction or realization that was already subconsciously baking.