I was trying to start a discussion about "why bad things happen" if there is a god (i'm an atheist/agnostic). This was a bad way going about it...
Oh, you wanker.

And here I was being civil. Enough with that then.
Let's get right to the point shall we. Suppose that God did create the Universe. And suppose that he also created the devil.
What allows Christians to differentiate the word of God from that of the Devil?
In the oft-cited "proof for the existence of God", the questions are usually "Where did the Universe come from?", and the lack of a solid answer is seen as proof. But, as said above, supposing that God did create the Universe, what proof is there that he stuck around?
The bible is full of the actions of a tyrannical, vengeful, and petty god. Not a loving god sold to you in a pretty wrapper, but a god of murder, rape, genocide, torture, and intolerance. A parasitic god that demands worship, if for no other reason that to feed its existence (or its clergy).
If God had moved on to other projects after creating the Universe, and the devil stepped in to assume his identity, how exactly would one identify 'the father of lies'.
In Mark 7:8-13, Jesus advocates the Old Testament punishment of murder for children who speak back to their parents. Is this the word of a forgiving savior?
And Revelation is like a party in your mouth, except everyone is being horribly tortured and drowned in blood, so you end up drooling on yourself a little and ruining your favorite sweater.
The bible itself is better evidence (to use the word in the loose manner of the religious) for the abdication of a benevolent god than it is for the reign of one. And the devil, as portrayed, seems like the kind of fellow to introduce himself early on (you know, that whole freakshow in the garden), breaking the fourth wall by writing himself into the story.
And the thing about stories where the author has written himself into them... they're usually poorly done and hard to swallow.
Just like Religion. (and clerical wang)