I saw a person, presumably Catholic, with a t-shirt that said, “If God created shadows it was to better emphasize the light”. The quote was attributed to Pope John XXIII. In some ways this is a quite conventional "contrast" argument, but in other ways it is amazingly cynical. I guess I am not surprised that adherents don't see the difficulty, but to recovering former Catholics like myself, the glaring issue is the shadiness of the sentiment. In essence it is saying (if it is saying anything at all) that this pope believes god allows things like mass murderers who torture people to death, so that he can let us know how good we have it. It is saying that god wanted a little accent lighting, so he decided that he would unleash vicious evil upon us so that we could recognize the good things in the world, when we weren't being victimized by evil.
It seems a remarkably bad cop-out for the existence of evil to say that it was put there just to help us better see non-evil. From whom else would we accept such an excuse. What if a sociopath claimed defense against his crimes of raping and murdering a little girl on the grounds that he just wanted to show people how, by following the opposite of his example (i.e. not raping and murdering) that they could be better people? Would we accept that this psychopath or his crime were necessary in order for us to grasp how to be good.
Furthermore, couldn't we argue that there have been more than enough examples throughout history of badness so that allowing even more of these to happen on a continuous basis, is not necessary, and does not communicate any kind of new message that has not been already amply demonstrated.
However, what I like most about the quote is that the pope didn't even commit to whether god created evil. He only speaks hypothetically, and then presumes to know god's motivation for an action which God might not even have taken. Nobody does double talk more blatantly than theologians.