Finding out that everything I believed as a Jehovah's Witness was a lie started a process of questioning that inevitability led to my becoming an atheist. I had accepted so many things that turned out not to be true that it made me question everything. It was not immediate, it was probably five years from when I left the religion that I realized I no longer believed in God. I did not come to this realization lightly, I actually wanted to still believe in God. But things arent true just because you want them to be, and I couldn't fool myself. I had worked to hard to rid myself of one flawed belief system to blindly still believe in another. I realized that I had believed in God because from a very early age I had been told he existed, that is all. Just as people born in Muslim countries believe in Allah, I believed in Jehovah because I was born in a Christian country. I found, when I looked at it objectively, that I could no longer see any evidence of God's existence. It's like you have seen the man behind the curtain and you cannot just unsee him and pretend everything is normal, it just doesn't work like that.
It's like if someone came up to you and told you about the wonders of Pink Unicorn, how happy it makes them, how they have such a great relationship with Pink Unicorn.But.....they have never actually seen Pink Uniicorn, they feel him in their heart and Oh My! if you just believe, you will feel him too. I had seen the error of accepting something simply because others were convinced, I just couldn't go there again.
I've heard many times from believers that Atheists just do not believe in God because they want to do bad, or they want to be selfish. I can tell you that is is a common misconception. I am more moral now than when I was a JW, because I don't make the mistake of substituting someone else's idea of morality for my own.