How does that work?
Very well!
Rudder, the content of their protest is their business. Concentrate on the freedome of speach issues.
"...How does that work?"
It originated with the idea of animal sacrifice to atone for sins. When we sin (lying, cheating, stealing, murder) we adversely affect those around us who are innocent of any wrongdoing. Traditionally, the animal that was sacrificed was often a pet of the family, such as a sweet, innocent lamb. The lambs were sacrificed to teach people that no matter what we do, when we sin, the innocent suffer, and symbolically, the lamb bore the brunt of their sins just as the innocent people around them were affected by sin.
Enter Jesus Christ, aka "The Lamb of God." Blameless. Innocent. Unblemished. Sinless. Sacrificed for the sins of all humanity so that those who claim that sacrifice and believe in it are forgiven of their sins for all time, a parallel to the Jewish tradition of sacrificing an innocent lamb to atone for sin.
This explanation may or may not make any sense to you, but that's the way Christians see the sacrifice of Jesus Christ on the cross. At least that's how I see it.
I don't believe God demanded sacrifice because he enjoyed killing innocent animals. He demanded it to show in concrete terms to people that sinning affects those around us, and that the innocent suffer when we sin. Jesus Christ was the final, innocent sacrifice, and no other sacrifices were needed to atone for sin after his sacrifice.