The Necessity of Penal Substitution
Gerald O’Collins and many other modern scholars hate the idea of Christ’s death as Penal Substitution. O’Collins states,
“… the way Aquinas adjusted Anselm’s theory of satisfaction helped open the door to a sad version of redemption: Christ as a penal substitute who was personally burdened with the sins of humanity, judged, condemned, and deservedly punished in our place.” 
Most people see this atonement model as being too violent. If God would punish his own Son in such a violent way then he must be an inherently angry God. A good rebuttal to this common critique of the historic doctrine of Penal Substitution has been given by Hans Boersma. He affirms, “… to insist on ‘pure hospitality’ in an impure world would mean to give it over to the forces of inhospitality and violence.” 
God is not angry for no reason. His perfect world has been overcome with evil and sin. According to Boersma if God decided not to deal with the injustice of evil in the world then violence and evil would reign. Anselm says,
“… sinfulness is in a position of greater freedom, if it is forgiven through mercy alone, than righteousness – and this seems extremely unfitting. And the incongruity extends even further: it makes sinfulness resemble God. For, just as God is subject to no law, the same is the case with sinfulness.” 
If God did not judge evil then he would be placing evil on an even plane with himself. By demonstrating a pure hospitality God would be handing over his authority over the world to Satan. This passive god is not the God of Christianity. Our God is our Father who shows his loving care for us by punishing us in order to remake us into his image. The author of the Hebrews confirms this,
“It is for discipline that you have to endure. God is treating you as sons. For what son is there whom his father does not discipline? If you are left without discipline, in which all have participated, then you are illegitimate children and not sons. Besides this, we have had earthly fathers who disciplined us and we respected them. Shall we not much more be subject to the Father of spirits and live? For they disciplined us for a short time as it seemed best to them, but he disciplines us for our good, that we may share his holiness” (Hebrews 12:7-10).
Paul also tells us that our present sufferings are a participation in the suffering of Christ (2 Cor. 1:5). It is because God loved his Son and because he loves the world that he sent his Son to bear the punishment for sins. One must recognize also that reconciliation is the goal of suffering. God disciplines us “that we may share his holiness.” Those who have critiqued the Penal Substitution model for being too violent have not adequately dealt with the Biblical evidence.
 Gerald O’Collins, Jesus Our Redeemer: A Christian Approach to Salvation, (New York, NY: Oxford University Press, 2007), 137.
 Hans Boersma, Violence, Hospitality, and the Cross: Reappropriating the Atonement Tradition, (Grand Rapids, MI: Baker Academic, 2004), 93.
 Anselm of Canterbury, The Major Works. Edited by Brian Davies and G.R. Evans, (New York, NY: Oxford University Press, 1998), 284.