Well first off, I will let you all know that I do not believe there is a god... not to say that believing in god is a bad thing. In my experience most people that have a strong faith and live their life in hope of having god's approval are generally happy and caring people. I think this is because they all have hope that there is something to strive for in hopes of going to a "better place" after this life. It is my belief that we live our lives on this planet for the sole purpose of continuing on life- not our own personal life, but life in general. I really don't think there is anything more to life than that purpose. I think many people want so badly to feel that there is something more to life, that there is some greater purpose, that they grasp onto the idea of our creator, god. Now, just because I believe this doesn't mean that I am a mean or evil person. I try my best to be accepting and friendly to everyone I come into contact with, and I do this for my own benefit. I am not trying to live my life according to someone else's arranged set of rules.
I think that religion was invented for a few reasons... my first belief is that religion was created in part to instill a fear of a higher power into people- hoping that humans would be more likely to behave themselves if they had a fear of the unknown. Fear of god is more likely to keep people "in line" than a fear of human authority. I believe that people developed a set of rules that they decided were moral and correct and spread the rules as the word of god, thinking that this way people would be more likely to follow these rules, and claiming that disobeying these rules would be considered a sin and would hurt your chances of earning a place in heaven, causing a person to instead spend eternity in the fiery pits of hell. Of course, not all religions are the same, and some religions don't encourage the belief in hell. Some religions instead enforce the belief that if one's life is not led in a holy enough fashion, that person's soul would be forced to repeat a life on this world in a different body, possibly returning in a body which is not even in human form, until they live their life in an acceptable enough manner to reach eternal bliss.
The second reason that I believe god was created by human imagination is that the belief of god dates back ages, and science and the study of the universe was not advanced enough to explain normal occurrences of nature. I think that humans felt uncomfortable in not knowing and decided that these unexplained occurrences, some as simple as rain, could best be described in saying that a higher power was at work.
In a related idea, the belief of god in conjunction with an afterlife helps people to cope with death. I know that the idea that your dead loved one is happier now than he/she was on this material world is comforting, in some cases comforting enough that the death transition from this world to the next plane of existence is treated as a celebration of that person's life in liu of a tragedy (the tragedy of the end of their life as well as the tragedy their death has caused in one's own). I think the "he is in heaven now" story is equivalent to telling a young boy that his dead dog ran away, and I think the idea developed under a similar motivation. It's as if all of the adults of the world died without ever telling their children there was no Santa Claus.
Another fact that I believe supports my beliefs is the fact that different cultures-- people who developed in groups entirely separated from other groups, all have different versions of this "higher power". One group of people who developed entirely secluded from another group, perhaps by a different continent would have completely different versions of religion. Some cultures believed that there was one entity who was to be worshipped and obeyed, while a totally separate group would believe that this higher power consisted of many different entities, all to be honored and feared, and each responsible for a different part of the world humans live in. If there truly was a god, why would this entity allow different people to derive their own versions of what he might be like, and what rules he expects humans to follow in their lifetime.
Obviously I am not a devil worshipper, so none of you christians out there worry your little heads off. I would be a hypocrite to believe that there is a higher power out there known as satan, but not believe in his counterpart, god... so just for the record I believe that satan worshipers are just as incorrect as christians, and all other religions.
How did I cope with coming up with all of these conclusions? Well, I'll tell you - it was damn hard. I was raised to be religious. When I began to doubt in god's existence, I felt fear every time I drove by the church. I went to private religious school for 8 years. I went to church every Sunday and sometimes on week days. I prayed every night (minimum). I was in the youth group. I went to religious retreats. I truly believed in every aspect. Nothing catastrophic happened to make me begin to doubt god's existence. Nothing happened to make me angry at god. I think people who shun god out of anger are doing so for the wrong reasons, and will only live to feel guilty the rest of their lives. Deep inside, they fear his wrath. Since the belief that rejecting god is highly known to be cause enough to go to hell, it was very hard for me to be sure enough in my convictions to actually do it. I can see how people that are unsure take the safe route - if they're right, they go to heaven. If they're wrong, no big thing. In my case, if I'm wrong, I will certainly go to hell (even though I am a very moral, just, honest, loyal person - silly rules), but that is the risk I take for following my true beliefs - those based on logic.
(and if it makes you feel any better, just be like my Mom, and instead of viewing the above statements as logical thoughts and conclusions, remember that it's really just the devil speaking through me.)