When I push this “button” on Calvinism to a Calvinist he or she usually retreats into voluntarism—the idea promoted by Duns Scotus and Ulrich Zwingli (among others) that God is above all law, meaning our intuitions about “the good” do not apply to God at all, and whatever God does is good simply because God does it.
I always wonder who these nameless Calvinists are. Somehow I doubt he picks on Reformed philosophers.
My frequent, almost constant, experience has been that, under such questioning, most Calvinists eventually wither and either simply appeal to “mystery” or “paradox” (admitting they don’t know what “good” means other than “what God does”) or give up and adjust their Calvinism to the point of disappearance (as in so-called “evangelical Calvinism”). Or, in many cases, they ponder and then, after a time, admit they can no longer embrace Calvinism. The few that steadfastly remain classical, high Calvinists (i.e., “TULIP” Calvinists) usually admit that they really embrace divine voluntarism—that God has no eternal, governing, moral character but does whatever he chooses to do and that whatever he choose to do is good just because he does it. What they rarely, if ever, admit (but must admit if they are to believe coherently) is that, in that case, “God is good” is only a tautology and therefore meaningless.
Once again, nameless Calvinists.
And he accuses "most" of them in his "almost constant" experience of retreating in to mystery or paradox.
But having said that, notice how he responds when a sympathetic questioners puts him on the spot:
Thanks, Tim. This raises the age old question of theodicy. I struggle with it mightily, very deeply. It troubles me all the time. I do lose sleep over it--especially when I see (on television or in the news) children being kidnapped, tortured, killed, abused, etc. I have sought help with this. The best help I have found is in Greg Boyd's "Spiritual Warfare Worldview." The best guide to that (because it does not rely on open theism) is his book Is God to Blame? Maybe it won't work for everyone, but it certainly has helped me. I think that when it comes to evil and innocent suffering (e.g., children) God is always doing the best that he can given the circumstances. But only God knows the rules; he has not chosen to reveal them to us but simply asked us to trust in his goodness. I do that. If God is not good, then he might be the one harming the children. If God is not omnipotent, there is no hope for a better world (as ours is getting worse all the time). I believe (with Greg) that God has given us prayer as our means of helping God help the victims. We are also called, of course, to take direct and indirect action to help free them from oppression and harm. But God has chosen not to do this (for now) all by himself. And human sinful rebellion has pushed God away so that this world is not as God wants it to be and will remake it to be in the end. I know of no better answer. All the other answer I have considered fall short either with regard to a moral order of the cosmos, God's goodness, or God's omnipotence. In short, the answer lies somewhere in God's self-limitation in relation to creation.
In other words, it's okay for Arminians to play the mystery card, but if a Calvinist plays the same card, that's cheating!