If everyone followed "an eye for an eye, and a tooth for a tooth" we'd all be left blind with toothless smiles.
I saw that somewhere, and it's true.
But, Christians aren't push-overs or doormats, we just have a Higher Power to answer to when we have been hurt. We also know that God will avenge us, He will make "our enemies our footstools".
In extreme circumstances such as murder, we are allowed to feel whatever feelings come up whether it be anger, or whatever. God doesn't want us to not have feelings. But to trust in Him. Yes, I would hate the person who killed my parents b/c that is a natural feeling. I might want to seek revenge, but will I?? I don't know probably not, I'd probably trust God to avenge me, and leave the punishment to God and the state authorities.