How could you claim to not believe in God when you didn't read everything about the early church, the entire Catechism of the church, Padre Pio, Saint Francis....people who spoke with God... People gained so much from belief in God and had tremendous experiences!
I believe that this argument fails for many reasons.
The argument from utility that is underlying the final part of the above argument does nothing to prove that the claims being made by Christianity are true. I cover this more in depth here. People can gain great insight from Christianity, great, but this doesn't suggest that their beliefs are true.
We don't need to read everything or completely exhaust all sources of information before rejecting claims being made by people. There are millions of things we don't believe in such as unicorns, faeries, leprechauns, etc. Do we need to read the encyclopedia of unicorns and read all of the books written by unicorn believers before rejecting the claims that are made? Of course not. We don't need to search every corner of the universe before we reject the claims made by unicorn believers. With the current knowledge and arguments that are on the proverbial table, we reject the claims made by unicorn and God believers because they are insufficient.
After using the analogy of unicorns and even other religious claims, my "opponent" told me that God is more important than unicorns and other religions and followed up with "it is so foolish to reject God because he is greater than anything that possibly can exist." I told him that that's just a subjective judgment and it doesn't matter anyway because I wouldn't accept something even if it were greater than anything imaginable because there's no good reason to believe it. This seemed to be a watered down version of Pascal's Wager.
I used another analogy like this:
Imagine that someone comes to you claiming that if you take his water medicine that you'll be cured of your medical maladies. You can reject his claim without reading all books on homeopathy and hearing from all people who believe the someone. Homeopaths make very specific claims and we can reject them because there is no good reason to accept the claims.
Although I dictated that I read arguments for and against theism, listened to numerous debates, had so many conversations...apparently, that's not enough if you didn't read "x and x." Well, it is. We don't need to exhaust all possible sources of knowledge or testimony before rejecting claims.
We don't accept the claims that people are abducted by aliens, people talk to the dead, tarot cards are reliable, Bigfoot exists.... and we don't need to read all of what's out there to be on firm ground.