[Matt R.]

Most religions would say God is all-knowing. An all-knowing God can of course "think" whatever he wants to. Further, I would argue that simply creating a being with free will allows the possibility of evil. The creator of said being doesn't even have to consider the possibility of evil -- it's ingrained in the notion of free will.

Also, as to your John example, I would argue that John is far from perfect if he does not consider the possibilities of evil. If John cannot even consider a simple dichotomy such as good vs. evil he would have to be mentally deficient in some way, or lack complete free will.