I don't suppose I am a complete pacifist; if you drew a spectrum I'm not sure where I'd sit. I do however understand that violence is a failure of peacemaking, war a failure of diplomacy. Sometimes that's because someone was not interested in peace, and sometimes that means that second best must be turned to.
But in the lives of most of us, for most of the time, violence of behaviour or rhetoric means that violence grows, violence wins. In argument, in relationships, there can be another way. And in public policy, we can lobby for better ways.
The story of Cain and Abel has a strange end - the warning that Cain would be avenged seven times if he were killed (Genesis 4:15). It is still a limit on revenge, and it is declared by God. It does stress the sanctity of life. And it is from an age of violence.
So when Lamech himself proclaims a much larger vengeance, and an unbalanced one, for it was death for a wounding and not death for death, we see how retribution can go so wrong (verses 23-24). Vengeance, not justice is in view. The image of God in chapter 1 seems not to extend to Lamech's victim. In many Ancient Near Eastern contexts, the image of God was limited to the nobility or king. In Hebrew thought, murder was denied because all are in the image of God.
Comparing Rwanda to South Africa, we see how the pursuit of truth and reconciliation trumps revenge. While due process and punishment are often appropriate, simply locking someone up or taking their life is not enough, when reconciliation and restorative justice can bring more closure, greater peace, and an end to the desire for revenge. This isn't being soft on law and order, but simply seeking a better order.
As long as there is sin there will be prisons, but for the every day of our relationships, we lock ourselves in prisons of anger and unforgiveness if we want to pursue vengeance for ourselves. God promises to repay. There are authorities to trust in. Sometimes we just let go, other times we actively seek reconciliation. But if our words and actions turn violent, it can only spiral in one direction. And Jesus died, not so individuals can wield weapons and words of anger, but so we can be agents of peace.