Believing or unbelieving is the less important issue: religion is a set of rules that make some people act like retards from the bronze age, that's the biggest issue IMO. I am an Atheist, but if somebody tells me that he's not 100% satisfied with the answers science gives him/her, well I don't agree, science is on a beautiful journey, but hey that's OK, and that's a Deist, somebody who believes a god created everything, but that same god stays the fuck out of people's lives.
Theism, which is the belief that a god not only created everything, but constantly watches over us and determines the outcome of everything, is just a manifestation of the human beings' egocentric nature: "oh yes, I am humble, I am nothing compared to god... BUT he cares about me to the point that he goes apeshit if I eat meat on Easter Friday or if I decide to work on Friday (or Saturday or Sunday)". That's bullshit: how egocentric, paranoid and arrogant is a person who thinks that?