One of the most central elements of Christianity is the atonement. There has never been a consensus among Christians as to what it means and how it works. The dominant view today is the Penal Substitutionary Theory (PST), according to which men had sinned and God could not excuse these sinners because he is perfectly just. Once sin has been punished, God can forgive. Jesus vicariously bore the sins of men and took upon himself the wrath of God. Jesus suffered for our sins.
This theory of the atonement is illogical, immoral, and incoherent; therefore absurd. If the atonement cannot be defended, then Christianity is false.
It is Illogical
Punishment is an appropriate response to immoral deeds, and we express condemnation of the person punished. Since punishment is only justified by guilt, only the guilty party should be punished. The infliction of suffering on a person is only properly described as “punishment” if that person is guilty. One cannot honestly express condemnation on someone who one does not take to be worthy of condemnation. Thus, it is impossible logically to punish an innocent person. Therefore, PST is conceptually defective and unintelligible.
It is Immoral
According to humane ethics and modern law, it is wrong for an innocent person to suffer in the place of the guilty; therefore PST is immoral. The following Bible-verse agrees: “The soul who sins is the one who will die. The son will not share the guilt of the father, nor will the father share the guilt of the son. The righteousness of the righteous man will be credited to him, and the wickedness of the wicked will be charged against him.” (Ezek. 18:20).
The Bible also teaches that Jesus (innocent) suffered in the place of sinners (guilty). Christians have to either admit that the Bible is contradictory or that God is not perfectly just.
Theologians have tried to explain the justice of Penal Substitution through the concept of imputation: man's sins were put on Jesus' account. In a grand accounting scheme, God transferred the debt of man's sins to Jesus, and then he paid the debt that was owed. Men sinned and God was angry. So, he took the sins of humanity upon himself and then suffered the penalty for them, so that he could forgive humanity for their sins.
But, in order for imputation of guilt to be justified, there has to be complicity or culpability by the one to whom the guilt is imputed. For example: the owners of a company are responsible for actions that happen within the company rules and consent of management. However, the company would need to be involved in the action. One employee murdering another in a fit of temper, for example, would not make the owners of the company guilty of the crime. It would have happened without their consent and against company rules. However, drugs manufactured that are found to cause death would make the company and its owners liable. Guilt would rightly be imputed – because the company's consent to the manufacture.
If somehow the guilt of humankind was imputed to Jesus, then God becomes guilty of sin himself. This solves the problem of Penal Substitution, but destroys Christianity. Theologians try to avoid this problem by claiming that, while the guilt and penal consequences (reatus poena) of men's sins were transferred to Jesus, the detriment of sin (reatus culpae) was not.
But this is impossible because guilt and detriment cannot be decoupled; without detriment there is nothing for which to be guilty. Thus, in order to defend penal Substitution, Christianity must have either an unjust Father or a sinful Savior. Either one destroys Christianity.
The death of Jesus is a human sacrifice. The Bible contains no prohibitions, but God explicitly approves of human sacrifices to himself (Leviticus, 27:28-29), and God's command to Abraham to offer up Isaac (Genesis, 22) is further evidence that human sacrifice is, at least in principle, acceptable.
Theologians have argued that it was never God's intention for Abraham to murder his son, but that he was testing Abraham's faith. This view, carried to its logical conclusion, make the atonement of Jesus immoral. If human sacrifice is unacceptable to God, then the sacrificial death of Jesus is unacceptable. Thus, the intellectually honest Christian must maintain that human sacrifice is moral, or else s/he rejects a fundamental doctrine of Christianity. The doctrine of Atonement is based on the rite of human sacrifice, which is an immoral and barbaric practice.
It Is Incoherent
The doctrine of Penal Substitution contradicts other core doctrines of Christianity. According to the doctrine of the Trinity, the Father, the Son, and the Holy Spirit are all equally God and share precisely the same attributes.
So, God was angry because men sinned. He had to punish them. The only way he could think of was this: He impregnated a woman and became the father of himself. As a man, named Jesus, he took on himself the sins of humanity and died on a cross. He extinguished his wrath by punishing himself; he sacrificed himself to himself.
There are two natures in the person of Jesus Christ; he is both divine and human at the same time. If divine nature cannot die or suffer, then it cannot pay the penalty for sins. Thus, when Jesus died on the cross, it was not his divinity that suffered, but his humanity.
Theologians argue that Jesus suffered a spiritual death, in which he was cut off from the presence and blessing of his Father. But, how can God separate himself from himself? And, if a separation from God is Hell, then did God torture himself for three days?
Credit to Dr. Ken Pulliam
See Chapter 7: "The Absurdity of the Atonement", in Loftus, J. (ed.)(2011). The End of Christianity. USA: Prometheus Books.