Pruss' Argument From Forgiveness

To my mind, there are few contemporary philosophers of religion who are more inventive than Alexander Pruss of Baylor University. Though he knows the classical arguments of philosophy of religion well (cosmological, ontological, etc.), he's also constantly creating new arguments for theism. I find his creativity inspiring, and also very instructive for budding undergraduate philosophers (like those frequently found lunching every odd-dated Wednesday in the Providence cafeteria).

Back in September, Pruss posted an interesting argument from forgiveness that I think is worth pondering. It's reprinted below (click here to go to the original post, which includes follow-up comments).

1. (Premise) If one has done a wrong, one ought to ask someone for forgiveness of it.
2. (Premise) If God does not exist, there are some wrongs (e.g., the murder of someone who has no friends or relatives) that one cannot appropriately ask anyone for forgiveness of.
3. (Premise) If one ought to do something, then one can appropriately do it.
4. Therefore, if God does not exist, there are some things one ought to do but cannot appropriately do. (By 1 and 2).
5. Therefore, God exists. (By 3 and 4).

Thoughts?