You have to understand what death is... In God's presence, all is sustained. Without, all is subject to death and decay. God, the absolute authority, cannot justly tolerate disobedience therefore the wages of sin is death. Christ did not sin, and yet was subject to death. He was forsaken that dark day, as far as his human frame could tell. It was an infinite injustice, yet by it we are "in" him eternally. He was made responsible for our sin, bearing the consequences so that all who are in him could be spared. The passover atonement was established as a pattern for thousands of years prior, and was absolutely necessary for anyone to be able to come before God, as we do now. He was the lamb of God, and from our angle, is all of God that we can see, God with Us.
So, take the ancient superstitious tribal practice of declaring/blaming all evils upon a goat, taking the goat outside the village, and slaughtering it ("scapegoating"), replace goat with human for a dash of human sacrifice, and tada?
Plus, Christ, being god, knew he would be put up on a cross, and knew he would be resurrected... unless he wasn't god? Actually, yeah, wait, I'm confused. He is part of the holy trinity, and knew he would be sacrificed, yet he thought god has forsaken him? Did he lose his magic god powers on the cross?
Also, did you just say that god has committed infinite injustice?
The father/son dynamic is crucial to sorting this stuff out in a logical manner. Of course God of the Universe couldn't wholly incarnate as a small child, but a human born without sin, walking in full obedience and with the full measure of God's spirit, could be as clear a picture of God as a human can behold, and the effects of his day to day life would profoundly shape history, before and after, IMHO. EDIT: Further, he was raised up the right hand of the throne, in eternity, which is why he could say, "before Abraham was 'I AM." EDIT2: Yes this creates a time quandary. The Bible is full of them. Either God is sufficient to solve them, or your God is not big enough.
You're going to love this. It's by sin that death entered, and by death affecting Christ who was without sin, death itself will be judged and destroyed. In the eternal, it is justified by its ends, but the injustice of it belongs to the temporal anomaly known as death.