Why people refuse to believe God exist

There are alot of Christian topic being formed all around but no one has yet said their reasons why they don't believe in God.

Is it just because you can't see God that you feel he don't exist, or because you feel nothing should be greater than humans, or you don't just want to believe God exist?

I call myself an atheist, but really, the only concept I vehemently disbelieve in is the idea of an omniscient, omnipotent, omnibenevolent deity. The existence of such a deity is disproven by the fact that events such as the Holocaust have been allowed to occur in human history.

As to the existence any other sort of deity, I'm agnostic, but as Soulreaper said, there seems little point in speculating about matters that are far beyond our capacity of understanding at this point. I'd rather focus on solving problems of the here and now.