Capital punishment is/was considered a deterrent because we are programmed to attempt to avoid premature death by natural selection. That's not to say people a

Capital punishment is/was considered a deterrent because we are programmed to attempt to avoid premature death by natural selection. That's not to say people always understood this or even that today it is the way most people think about it, but at least according to a mechanistic/biological view of behavior, that is the basis. Note that natural selection did NOT necessarily put a desire to pass on our genes into us, since that wasn't necessary. It simply put such things as a desire to continue living, a drive to care for children (which can easily be transferred to non-biological children, and we can easily ignore that drive for biological children that we don't bond to), and a drive to have sex.