When we approach the New Testament with "mercy not sacrifice" as our rightful frame of reference, the notion of penal substitution is seen for what it is–something like an Aztec or Greek ("pagan") notion.
Atonement in this sense is like the Pharmakos. In Ancient Greek religion, Pharmakos (where we get pharmacology) was a kind of scapegoat. Pharmakoi were selected usually because of some physical deformity. They were kept, feed well, until the first day of the Thargelia, a festival of Apollo. Then one was chosen by lot, was led out of the city, and sacrificed as expiation. This would purify the people and the city.
On the other hand true "Atonement" is a fulfillment of the biblical priestly liturgy. This liturgy always pointed to something radically beyond itself, namely, a "sacrifice" born of love that subverts and unmasks all sacrificing.
This frame of reference, "mercy not sacrifice", is crucial for nothing short of the "rebirth" of Christianity.