The problem is that we are in thrall to subordinate forces just as Adam and Eve were, and for which originating sin they were expelled from the Garden. In our case, these forces are fear and anger, both of which render us incapable of love. They are our emotions, they originate within us, but we project them onto other individuals, groups and nations. We need these others. For us to be good, someone has to be bad.
When something terrible happens, ego demands that someone be punished. In simpler times, they used a proxy. Two kids were pulled from the goatherd. One had its throat slit, the other was driven into the desert, taking with it all the sins of the community.