The problem of evil is an interesting one, in that you can take it two ways. On the one hand you might call it an internal problem to theism. Something like: "the Christian understanding of evil is incompatible with the Christian conception of God", and that's the argument Plantinga is primary addressing (that theism is not incoherent or internally inconsistent on this matter)
But you can also take it as an external problem - that theism doesn't do a good job of explaining the existence of evil. In my mind this is a stronger argument, but what sometimes gets lost in the discussion is that the problem doesn't go away if you discard theism. If evil really does exist what alternative worldview does a better job of explaining it?
That evil is just a social convention created by minds produced by random processes geared towards evolutionary fitness?
Maybe. But doesn't that just explain away the problem by stating evil doesn't really exist? (at least not the kind of evil suggested by Christians?) And if it doesn't really exist, how can you use it as an external argument against theism?