We're told that Cain and Abel, the sons of the parents of the human race, went into the family business farming and tending the flocks. Both, in the fullness of time, made their offerings to God, but God did not respond to Cain's offer, didn't even receive it or comment on it. But he lavishly thanked Abel. He then acted on the rage and slew his brother Abel. The legacy of that murder is that whenever blood is shed, it cries out from the ground.
Murder is wrong.
It is obvious that part of spiritual maturity is learning to name one's anger and to find a place to take it, or a willing ear to hear it. We have the capacity and as the long narrative of scripture makes clear, the obligation to reign in anger and destructive drives. This is the line, and we may not cross it. All civilized and maturing people have always agreed to this. That, along with our penchant for making ourselves victims, has blurred the line that God has drawn.