An awful lot of atheist arguments seem to rely on the omnibenevolence of God.
"If God is omnibenevolent then..." [the world wouldn't be the way that it clearly is]
Is God omnibenevolent?
Where does it say so?
How do we know this from experience?
The other part of the argument is often omnipotence. The argument often goes like:
"If God is omnibenevolent and omnipotent then why is there suffering?"
I'm afraid I find that line of reasoning fairly compelling. But I don't conclude from that that there is no God, only that maybe he isn't either omnibenevolent or omnipotent...