The difference between an atheist and monotheist is just
one god. Monotheists don't believe in any gods, except for the one they were told to accept as
God by their parents, an accident of birth so to speak (usually 99.9% of the time anyway). The atheist looks at the god he was given (by parents, nation, or culture) and says, "How is this one any better than the rest you didn't want me to believe in anyway?"
Jokes aside, people like myself became atheist because of the dogmatic and abusive nature of the religion we grew up with. To this day I have to
around members of my family who are still believers, often leaving the room when they discuss their religion in order to avoid hearing things that would make me angry. If anyone thinks that is extreme, then you have no idea just how much fiendishly twisted religious indoctrination can entrap the minds of believers. I consider myself a "live and let live" sort of person. There are those who call themselves 'atheist' and follow secular ideologies with totalitarian doctrines. They scare me as much as the religious Fundamentalists. Lately I'd call myself agnostic, but I'm also very open minded to understanding deities in the Universe.