One problem I can see with this argument is that we are presupposing that there is some criteria of goodness independent of our knowledge, which constitute those "factors that we don't know about". However, it would seem that these criteria cannot hinge upon God, as in the traditional Christian definition—that whatever God wills is good—because this leads to circularity.

Alternatively, one could adopt an independent definition of goodness, and attribute these factors elsewhere. For instance, we can say that goodness is that which results in the maximal happiness possible, all else being equal, and that God, of course, knows something we do not, which affects the sum total of happiness. These sorts of arguments essentially express the idea that God lets evil happen for a greater good. However, many would argue that this is un unjustified belief. Certainly, while I agree that many evils which did happen had some positive effects down the road (for instance, the Holocaust arguably leading to international sympathy for a Jewish state), it is not apparent that this is necessarily the case every time evil happens. Moreover one may reasonably think that this is a highly problematic belief; see, for instance, condemnations drawn by religious figures when they claim that some natural disaster happened for a greater good.

Another problem with this argument is the assumption that free will is a good thing. For surely if there being free will is not morally better than there not being free will, then a world in which there is no free will and no evil is better than a world in which there is free will and evil. Thus we must defend the thesis that there being free will is morally better than there not being evil. Of course it might seem that any reasonable agent would prefer to make her own choices than to have choices made for her, but this doesn't imply that there is any moral goodness to having this preference realized. So it seems that some further arguments ought to be addressed this way.