OK, someone explain the idea of a blood sacrifice so that it makes some sense. Is there any way to do that?

Sacrificing animals is cruel and stupid. Sacrificing a human is beyond cruel, and heading straight toward total lunacy. Before anyone spouts some garbage about forgiveness of sins, lets try this: Person wants sins forgiven, Person asks deity to forgive sins, deity (being omnipotent) knows person is sincere, Deity forgives sin. What is the blood and death crap about?