To answer the initial OP, for two reasons
(1) I truly believe that religion was created as a method of 'crowd control' before we had government/police/laws etc - it was a moral code for people to live by, and those who disobeyed were sinners, much as we now have a set of laws and those who disobey are criminals.
(2) Because I have never been given a difinitive answer to the questions I have regarding certain aspects of Christianity - Adam and Eve were created and had sons. How did that then evolve into more humans? ALSO....I understand why God, should he have existed, have put the Tree of Temptation in the garden, to test his creations, but why a talking snake? Surely one or the other? And why was the snake's punishment to 'crawl on your belly all your days'...erm, it's a snake? ALSO how can we think so highly of a creator who allows henious acts to happen on his planet? Life and death, yes, but murder, rape, paedophillia...if God created everything, he created the ability in some humans to carry out these acts. I have yet to be given an answer to the above that isn't "God acts in mysterious ways".
I also think that in my experience, atheists and agnostics tend to be a lot more acommodating and open-minded than those following a religion. Yes, there are exceptions to this rule, but ime, this tends to be the norm.