If God exists, why is there evil?
An omnipotent, omniscient, perfectly good God could prevent suffering and would want to. Yet earthquakes flatten cities, children die of cancer, and the holocaust happened. Either God can't, won't, or isn't there.
Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil?