Was born into a moderate Roman Catholic family. Never really questioned my faith but was not overly-religious until I was 13 years old, about to receive the sacrament of Confirmation.
At Confirmation, since your parents and the Roman Catholic Church decide your beliefs for you when you are too young to even pronounce your name correctly, you have to confirm that you do, in fact, believe in God. Age 13 is when the Roman Catholic Church believes you are old and mature and informed enough to make that decision, knowing full well that at 13 years old, you are still under the oppressive thumb of your parents.
So I had a friend who lived across the street and his father - a Scot - was a really nice guy. I wanted him to be my Confirmation sponsor (like a second godfather, someone dedicated to helping your faith grow. I actually took it seriously). So I asked him. Coming from a Portuguese family, my parents didn't like this and wanted that position - a very huge honour in Portuguese culture - to go to a family friend. They made me renounce my request to that nice, generous man.
That is when I began questioning the validity of the sacrament. The next year, I started high school. A girl had moved to my city from Steinbach, Manitoba. A hugely religious area. She was a fundamentalist Baptist and her father was a pastor/missionary. We liked each other. I was still largely apathetic toward religion, but she was fervent about it.
We started dating and she would constantly attack my Catholicism. She didn't even consider Catholics as Christians. And more out of tenacity and vanity, I vehemently defended Catholicism. It didn't take her very long to point out how absurd Catholicism is. This was Earth-shaking. This was a view I had been spoon-fed my entire life and hadn't bothered to question and now I find it was...wrong!?
Well she convinced me to be a Baptist and I was a fervent fundamentalist Baptist. I started praying, reading the Bible, going to Church with her secretly (because of parental opposition to Protestantism). I took all positive aspects of the Bible and tried to emulate them in my daily life. I tried to live as Jesus did and to be frank, it was like a placebo. A state of utter bliss, so I can certainly see the appeal of theists in that state of mind.
However, when she got me questioning my Catholicism, I started thinking "What if she's wrong too?". So I started questioning everything I was being told. I went on tons of Internet forums - including RF years ago - to gather different religious opinions and perspectives and beliefs. Information was my drug. I was starting to be convinced very easily. Why? Because when you don't form your beliefs based on evidence, logic, and reason, you can be easily swayed by anyone with a smooth tongue.
I had never considered agnosticism or atheism before because I always held the firm belief that something could not come from nothing and therefore, God must exist. I realize the faulty reasoning now. But this was my rationale at the time.
I had a firm belief that atheists simply misunderstood Christianity, so I signed up to forums called "The Ethical Atheist". My goal was to have them ask questions of Christianity and I would defend them as best I could. And while some questions they asked were legitimate misunderstandings, they began asking questions I had never thought of before, prompting a different way of thinking.
I began to see things through their eyes and things became much clearer. And it didn't take insults or aggressive posturing to do it. I was in a state of shock. I was faced with the grim reality of there being no God, but I had a deep psychological attachment to God. You can't go from being a fundamentalist Christian to atheist cold turkey.
And so, I would try to look myself in the mirror and utter phrases like "I hate God". After all, if I didn't believe in God, this would be no problem, right? But I was scared out of my wits to do it. I had a very real fear of roasting in Hell for eternity for saying such. Sometimes, I would burst into tears, begging for forgiveness from the invisible man in the sky for saying that...even if in my mind, I didn't think he existed. I was operating on some retarded form of Pascal's Wager.
After months and months of struggle I could finally say it without fear and the day I did, I had never felt so liberated in my life. It felt like a huge burden was off my shoulders. I had remained an agnostic for about a year. That is until I read Dawkins' The God Delusion.
That book destroyed all religious arguments I had, even some I never thought of, and some that were employed against me on Internet forums such as these. I began to see the world through a rational, evidence-based perspective and I loved it. Have never looked back since. It lured me out of agnosticism because the notion of God is highly improbable, even if we can't prove or disprove it scientifically.
Ever since then, I've never stopped questioning what people tell me, no matter who tells me it. And that's the way to think critically. I have never been happier than I have been as an atheist and humanist. And more intellectually fulfilled at that.