As an anti-theist, I'd like to share some views from the other side of the coin.
The reason that I believe what I believe is because, based on known and proven history and my own experiences with what I see every day, there is nothing else left to believe.
As you're all aware, atheism isn't about believing something, it's about not believing something. We all know this, because we're all atheists in one way or another. We all know what it's like to not believe in something. The tooth-fairy for example, or the belief in Thor or Wotan (for most of us).
My reasoning for being atheist stems, I think, from the the basic principal of what a mono-theist has to believe. Simply saying most of this stuff out loud, would insult a lot of people. This is because the very vocalization of what believers believe does sound as though it's being mocked. To an intelligent, logical person brought into existence 5 minutes ago, it would seem like insanity.
Our race, as we know it, is between 100,000 and 200,000 old. Let's say that for argument's sake that it's 100,000 years old. In order to be a Christian you HAVE to believe that for 98,000 years, all the pain and suffering our race went through, even just 10,000 years ago (most people dying in child birth, average life expectancy around 25-30, people dying of diseases from bacteria that they didn't know existed, famine, drought, natural disasters (all punishments as far as they were concerned)) was watched by God with complete indifference
Then 2,000 years ago he decided that enough was enough... it's time to intervene. And the best way to that was to condemn a man to a human sacrifice somewhere in the less literate parts of the middle-east (Not China where people can read and study evidence).
Don't quote me on the exact details of that but you obviously get the point. I don't believe it and I still can't get my head around the fact that a thinking person can believe it.
Where then, do my morals come from? They come, partly from genetics but mostly from the manner in which I was raised and the experiences I've had in life. I consider myself a decent and moral person. I've never committed a crime worth mentioning and if *IF* living a moral and decent life by my own standards in the only world we know that exists (the material one) sends me to hell, then so be it.
People will get defensive and start nit-picking on facts... don't. I don't care. You obviously get the gist.
No offense intended.