IMO, this article is as close as you will get to an answer:
http://johnmarkhicks.faithsite.com/content.asp?CID=7015
Quote from the article:
God does not satisfy a law higher than himself. God is not subservient to some higher principle. On the contrary, God's character is the highest principle in the universe. He owes nothing to no one (Job 41:11; Romans 11: 35).
The atonement was necessary because God determined that it was so.
Paidion posted:
George MacDonald wrote:
They say first, God must punish the sinner, for justice requires it; then they say he does not punish the sinner, but punishes a perfectly righteous man instead, attributes his righteousness to the sinner, and so continues just. Was there ever such a confusion, such an inversion of right and wrong! Justice could not treat a righteous man as an unrighteous; neither, if justice required the punishment of sin, could justice let the sinner go unpunished. To lay the pain upon the righteous in the name of justice is simply monstrous. No wonder unbelief is rampant. Believe in Moloch if you will, but call him Moloch, not Justice. Be sure that the thing that God gives, the righteousness that is of God, is a real thing, and not a contemptible legalism. Pray God I have no righteousness imputed to me. Let me be regarded as the sinner I am; for nothing will serve my need but to be made a righteous man, one that will no more sin. (Unspoken Sermons III, Righteousness)
MacDonald seems to know nothing of the concept that in the atonement both justice and mercy are served. What mercy! God took upon Himself the punishment we deserved! Glory to God!