It is useful to note that even if Plantinga or any Christian rejects the contra-argument, the first premise can be challenged. Rather than quibble with what is meant by maximal excellence, an atheist can accept the definition as it stands. The atheist can, however, question whether this is possible world W in where a being of maximal excellence exists and explore the consequences if it turns out that this isn’t that possible world. In other words, if this isn’t that specific possible world, then the argument is speaking of a possible world that is inaccessible to the believer and the believer is therefore in no better position to convince the non-believer. Put another way, if a being of maximal excellence doesn’t exist in this possible world, then it possibly exists in another world that cannot be accessed by any of the inhabitants in this world. There is therefore no utility or pragmatic value in belief. The argument would only speak of a logical possibility that is ontologically impossible in this world.
The atheist can take it a step further. What Christian theists purport to know about god stems from the Bible. The Bible, in other words, gives us information about god, his character, and his history as it relates to this world. Assuming this is possible world W, does he represent a being having maximal excellence? Is he, for instance, identical to a being who is wholly good? Any honest consideration of parts of the Bible would lead one to conclude that god is not identical to a being who is wholly good; god, in other words, isn’t wholly good. So obvious is his evil that Marcion of Sinope diverged from proto-Orthodox Christians in concluding that the Jewish God in the Old Testament is an evil deity and is in no way the father of Jesus. Yet if he’s evil, then he isn’t wholly good and if he isn’t wholly good, he fails to have maximal excellence.
Moreover, and much more damning to Plantinga’s argument, is that a being of maximal greatness has maximal excellence in all worlds. Therefore, if this being does not have maximal excellence in one of those worlds or more specifically, in this world, then it does not possess maximal greatness. Far from victorious, Plantinga’s argument would taste irreparable defeat and this, in more ways than one.