There are two main reasons I don't believe in god(s). The first is that I've never seen any eveidence that god(s) exist. I mean, the most popular reason for believing in god(s) is the argument from design. But we are taught early on to look for design, so we see design in places where it just doesn't exist. I mean, extraordinary claims require extraordinary evidence.
The second reason reason I don't believe in god(s) is the problem of evil. How can evil exist in a universe created by a benevolent (all-good) and omnipotent (all-powerful) god? Monotheists try to use the fall of Adam and Eve to justify this one, but why would god create a flawed creature he knew would sin and he knew he would have to punish? I mean, if he's omniscient (knows everything), he would have known that Adam and Eve would have sinned. And knowing his nature of not being able to stand sin, he would have known he would have to punish them to eternal "death".
I got a million reasons for not beleiving in Christianity, but this is about beleiving in god, not about believing in Jesus, the bible, etc. So I will save those objectionsfor another thread.
Btw, I have no problem with religion as long as people don't try to convert me (that is one of my biggest pet peeves). I do not mind discussing it with people, as long as the primary intention of both sides (me included) is to inform of our postion, not to push it on others. I hate the ideology that those who don't believe in a certain religion will go to hell or be eternally punished. When I finally die, I will be ready for the eternal rest.