This reminds me of what seems to me the most remarkable fact about Christianity: that it has no single theory of atonement. Christology, the Trinity etc. were argued over, viciously, for centuries, but why Jesus' sacrifice was necessary and how it was supposed to work has never been an important theological issue to most Christians, outside of a handful of theologians like Calvin. It's just been taken as a bare fact that the crucifixion happened and explaining its mechanics isn't that important.
Huh? It's a hotly debated topic. For example Catholicism states that one receives the benefit of Christ's atonement via the sacraments which is exactly why some fundamentalists attack them because they believe that renders Christ's sacrifice as insufficient.
Well this is my entire point: that's sacramental theology, not a theory of atonement. Whether one receives the benefits of Christ's atonement through sacraments or not says nothing about the mechanism of Christ's own atonement. That there's been more argument between denominations over how sacraments work for us than the nature of the crucifixion (again though maybe excepting Calvin, who did take a dogmatic approach to atonement that was influential) is what I think is remarkable about Christianity.