I read a book from a church library about sacred violence and non-sacred violence (nothing really is sacred about violence at all, I think.
Anyway, the book said that what they call sacred violence is that ok'd by the religious leaders. They said not only were animals sacrificed, but human adults and children were, too, by the old Hebrews as well as the other cultures around them. They said there would be internal discord in these groups, and sacrifices helped build internal group cohesiveness and "sprit de corps," much like people getting together today to rally around their favorite football game, I suppose.
The big point here, that the book was making, is that the leaders would tell the people that God told them to sacrifice, so the people wouldn't turn against the leaders. So, when Moses ordered 3000 Hebrews slaughtered because they made and worshiped the golden calf, he said God told him to have it done, so they wouldn't blame Moses.
I, myself, believe the Bible is filled with much of God's wisdom, but I can't believe it is the faultless, inerrant word directly from God because of these kinds of things in there. Seems to me Frank is right. Very human priests added a lot in there to validate sacrifice. I can't believe God told anyone to sacrifice thousands of his beautiful, precious animals who He must love as much as he loves humans.