Mike's response to the problem of evil: if evil disproves God, then the moral framework that makes evil "evil" also collapses, creating a self-defeating argument

Mike argues that if the problem of evil convinced him there was no God, he would then have no grounds to consider anything truly evil in the first place — atheism leads to nihilism and the collapse of moral realism. So using the awareness of evil to argue against God is self-defeating: you lose the framework needed to sustain the argument.