"Is God willing to prevent evil, but not able? Then he is not omnipotent.-Riddle of Epicurus
Is he able, but not willing? Then he is malevolent.
Is he both able and willing?
Then whence cometh evil?
Is he neither able nor willing?
Then why call him God?"
David Hume first posed these questions, in reference to an Epicurus citation (which may have been wrongly attributed to him in the first place), and it has become known as the Riddle of Epicurus. It is just as true today as in the times of Epicurus and in some might claim that today's world examples this argument against god even more so.
The evils of today stand out against our everyday society like black on white, and yet (and perhaps as a result) faith continues to grow. (At least the hateful and intolerant parts of it seem to) Against the backdrop of our day to day lives, evil exists on a level that many can't comprehend. On a level that riddles the mind with its ferociousness and tenacity for inflicting suffering on those who oppose it.
So how do we reconcile the concept of an all loving god, with the presence of vile and disgusting evils that should be far below his ability to stop?
Maybe it seem less convincing in David Hume's words, so lets break these words down ourselves.
Either God wants to abolish evil, and cannot; or he can, but does not want to.
If this is true, then he is either evil, impotent, or non-existent.
There is no other answer.
Many theists will claim that he is trying to teach us life lessons with the worlds evil, or that evil is OUR creation, but if it is a life lesson then he falls well below any moral standard that has ever been set by any culture in history. NO one would allow genocides, infanticide, genital mutilations, and senseless murder just to teach us a lesson.
What about the claim that evil is OUR creation made possible by the gift of free will? That still doesn't explain why he would create us with that ability. He knew what we would do in the world that he created from the moment he thought of creating us, but he did it anyway. So if he created us knowing that we would be this way, and did it anyway, then he did it purposefully. By purposefully I mean that since he designed us, and he knew that design would make us this way, that he actually designed us to be this way and to create the world we have now.
Making him evil once more.
This leaves only the last part...
If God can abolish evil, and God really wants to do it, why is there evil in the world?