I come at this issue as someone thoroughly committed to the doctrine of Penal Substitutionary Atonement. I think that's clearly in the Scriptures, and fairly central to our understanding of the Cross.
But it's definitely not all there is to say about the Cross. And as I was reading Torrance's The Trinitarian Faith, I really appreciated some of his elucidations ca. pp154-190.
Firstly, Torrance reminds us "that we cannot but think of the incarnation of the Son as falling within the being and life of God" (p155, emphasis original), and that this has significant implications for our understanding of the atonement. The atonement too was internal to the incarnate Christ; This is over and against the 'Arian' move which, in externalising the Son from the Father, made the atonement an external and extrinsic work.
Torrance presents a basically Athanasian connection between redemption and incarnation, and the focus on Christ's assumption of full, and representative, humanity, and his personal and ontological act on our behalf.
The danger of a PSA-theory that lacks appropriate integration with other key doctrines, I suggest is seen on p158:
"In that event [an Arian conception of the Son as a created and temporal being external to God] all relations between Jesus Christ and God could be construed only in external moral terms without any unifying centre in the Person of Christ who as God and man is the one mediator between God and man. That is to say, the atoning sacrifice of Christ would then be understood only in terms of some kind of superficial socio-moral or judicial transaction between God and mankind which does not penetrate into the ontological depths of human being or bear savingly upon the distorted and corrupt condition of man's actual human existence."
The danger of some PSA-presentations is exactly that superficial judicial transaction, which a robust doctrine of Trinity and Incarnation 'corrects'. God, in himself reconciles Man, whose nature he has assumed in the Son, to himself. There is something profoundly interior to the atonement.
Torrance goes on, "the understanding of the atonement in terms of the inner ontological relations between Christ and God and between Christ and mankind, implies that the very basis for a merely moral or legal account of atonement is itself part of the act state of affairs between man and God that needs to be set right" (p160).
Our very moral order, like the rest of creation and our very selves, has been corrupted by sin and is in need of redemption. The atonement not only redeems us in a legal sense, and a moral sense, but the very framework of morality must be redeemed.
"Within the moral order as it stands, as Gregory Nyssen saw [Or cat. 22], it would be irresponsible and immoral for one person to take the place of another" (p160). There is something about substitutionary atonement that should bother us, and no amount of bloody minded reinforcement takes away the fact that if one party substitutes in for a guilty one in a legal transaction in our systems, we would consider it a fundamental injustice. The way to come to terms with this is not to discard PSA, nor to consider the very doctrine to be immoral, but to understand that our very moral order is corrupt through our sin and in need of redemption, and that the singular and inexplicable work of God in Christ reconciling the world to himself is Good and defines the Good and restores the Good.
Torrance explains it thus, "In this interlocking of incarnation and atonement, and indeed of creation and redemption, there took place what might be called a 'soteriological suspension of ethics' in order to reground the whole moral order in God himself. This helps us understand why the main stress by Western theologians on forensic transactional accounts of the death of Christ was rather foreign to Greek partristic theology - not that it excluded forensic elements, as we shall see, but that they were held within a doctrine of atonement set at a deeper level." (p160-161).