Robert Adams raises and interesting objection to modal realism based on the problem of evil. He believes
[That] our very strong disapproval of the deliberate actualizing of evils… reflects a belief in the absolutely, and not just relatively, special status of the actual as such. Indeed, if we ask, “What is wrong with actualizing evils, since they will occur in some other possible world anyways if they don’t occur in this one?”, I doubt that the indexical theory can provide an answer which will be completely satisfying ethically.
Adams’ objection concerning the actualization of evil is irrelevant to a Thomistic version of modal realism (this version to be released in an upcoming paper in the Fall of 2012). Thomas does not seem to have any problem with the presence of evil. When discussing Boethius, a philosopher prompts the question, “If there is a God, how comes evil?” Thomas argues that the question should be reversed—“If there is evil, there is a God.” For there would be no evil, if the order of goodness were taken away, the privation of which is evil; and this order would not be, if God were not.