I can tell you what triggered me becoming an atheist.
I was reading a lot of Isaac Asimov books, including the non-fiction ones. I gained respect for him. After learning he was an atheist, it started being a possibility I considered. From there, I was able to figure out which possibility was right on my own.
This seems to be a trend. I never seriously worried about animals until joining felicifia.org where a lot of people do. I never seriously considered that wild animals' lives aren't worth living until I found out some of the people on there do. I think it's a lot harder to seriously consider an idea if nobody you respect holds it. Just knowing that a good portion of the population is atheist isn't enough. Once you know one person, it doesn't matter how many people hold the opposite opinion. You are now capable of considering it.
I didn't think unfriendly AI was a serious risk until I came here, but that might have been more about the arguments. I figured that an AI could just be programmed to do what you tell it to and nothing more (and from there can be given Asimov-style laws). It wasn't until I learned more about the nature of intelligence that I realized that that is not likely going to be easy. Intelligence is inherently goal-based, and it will maximize whatever utility function you give it.
Theism isn't about god. It has also social and therefore strong emotional consequences. If I stop being a theist, does it mean I will lose my friends, my family will become more cold to me, and I will lose an access to world's most wide social networks?
In such case the new required information isn't a disproved miracle or an essay on Occam's razor. That has zero impact on the social consequences. It's more important to get an evidence that there is a lot of atheists, they can be happy, and some of them are considered very cool even outside of atheist circl...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.