I come from a mainline, Black, protestant church. I have no bad memories of coming up in this tradition, really. I was personally acquainted with every minister and most of the bishops and church elders that we've had and enjoyed the company of all of them. I still do. Point of fact, I'm still somewhat involved with the church, having just discussed the latest internal politics with my aunt and my cousin, today. All that said, I can't believe what they ask me to believe. I reject Jesus Christ as my Lord and savior. They know this. But, to some extent, the Black church is more about community than it is about religion. And so there's that.
I'm not sure if it's correct to say that I ever "lost faith" really. I believed as a child, but I'm not sure if that should even count as genuine belief rather than as a belief that was the result of the sort of credulity with which a child approaches every claim of their parents/authority figures. My mother still, for example, enjoys telling the story of how I cried one Christmas, thinking that Santa wasn't going to come to visit me when I was something like 6 or 7. (It doesn't hurt that I was a particularly adorable child.) But I haven't believed in Santa since I was old enough to really think about it. The same goes for God.
I suppose that what really got me thinking at first was growing up in a somewhat religiously diverse community. My friends were Catholic, they were Jewish, they were Muslims. And the fact that the religious views that were being instilled in me necessitated that they (or at the very least the Jews and Muslims) be subject to eternal torment really forced me to take a more critical look at my faith. My friends weren't going to hell, were they?
I should also say that I've never, though I've prayed for it, had a personal experience of Christ. I can't talk about the inner witness of the Holy Spirit because I've never felt it. As such, I've had to go by the arguments for and against the existence of God. And, as far as I have been able to tell, these arguments firmly establish that there's no evidence of God's existence and that there's good evidence that God, at least as most monotheistic traditions conceive him, does not exist.
Actually, this lack of a personal experience of God, more than any particular argument, has been the most convincing disproof of his existence for me. I should say that, growing up, I lost some friends to gun violence. I suppose that it's not surprising that these deaths led me to questions of what the purpose of life is, whether there's life after death, etc. And while I prayed a lot on these topics, I received nothing in return. The silence was deafening. And I tend to take it into account any time someone tries to talk to me about their inner witness of God.
So, these days, I'm perfectly happy with saying that there probably is no god. I tend to think that I only have 80 or so years and I've used almost 30 of them. And I tend to think that I'm lucky to be here.