Logically speaking, the system is perfect.
Assumption 1: God demands justice
Assumption 2: God is merciful
Assumption 3: We are discussing the eternal not the temporal
Assumption 4: The entire human race is guilty
Using these basic assumptions, how does a perfect God satisfy the demand for perfect justice and at the same time exhibit perfect mercy?
I believe you already know the answer.
W.K.
Obviously the perfect solution is to visit harm on yet another innocent party - "the scapegoat". </sarcasm>
I can see at least 2 problems with your scenario. First, the assumption that all humans are guilty. Guilty of what? Are you referring to Original Sin? That's another very flawed parable, IMO. Basically we're guilty just for existing as humans in the first place. Well excuuuuuuuuuuuuuse me for living! I accept no guilt for the so-called crime of merely existing, nor for anything my distant ancestors may have done.
The second problem is the scapegoat. Just thinking off the top of my head, a rigorously just yet merciful response would simply entail forgiveness of whatever actual sins we as individuals commit, and for which we truly repent & try to pay back the damages. I think the whole idea of "mercy" is based on not enforcing one's right to restitution or revenge. It's simple, to the point, and deals with the debt the criminal owes to the victim. No 3rd parties need to become victims of the justice system. A much better system, IMO.