For any theists here who would like to have a better understanding of some of the reasons why atheists think there is most likely no god(s), this post at The Friendly Atheist gives 34 Unconvincing Arguments for God.
It's a pretty good post and I would like to have done a cut 'n paste of the arguments here, but I do not do extensive copying of others people's work if I do not have their explicit permission to do so, even if I give them proper attribution. It's just another pet peeve of mine.
So hop on over there and take a few minutes to read through the arguments. If you think you can refute any of them, it would make for a good discussion here and also give you some insight into the way some atheists think.