Without the capacity to do evil, being "good" is meaningless. If you couldn't do wrong, only right, you are merely acting by your nature, and so what you are doing isn't really "right", as doing what is right requires right intention, and not right behavior. Right?Will someone respond to my question about "God created man in his own image", for Pete's sake.
The same seems true of God. If God were only acting by his nature, why worship Him? If He could never act outside of "goodness", even if He willed it so, he'd be an automaton ("Please insert prayer HERE"), AND he wouldn't be omnipotent (as there would then be something impossible for Him to do). So, it seems like God has freewill; He can do evil. BUT, the difference between Him and us is that He has no problem avoiding sin (he is all-powerful and all-knowing, after all), whereas we can barely predict the next twenty minutes.
So we are created in His image, fully equipped with capacity to do both good and evil, but unlike Him, we are not all-powerful and all-knowing, so we cannot always make the "good" decision.
I hope that all made sense...I'm really tired...