Silver, you must be thinking of the following, from *The Book of Satan* by Anton LaVey:
"Hate your enemies with a whole heart, and if a man smite you on one cheek, SMASH him on the other..." III:7
Modern Satanists don't condone murder, because to do so in a civilized society is stupid -- and stupidity is the Number 1 "sin" in Satanism. If one is not prepared to face the consequences of one's actions, then one is not a Satanist. However, responsible retribution is not only condoned, but expected. Because the person who smites you first, had damn well better be prepared to face the consequences of such an action. Satanists do not "turn the other cheek."