If something is wrong, then it’s wrong all the time, not just when it suites your perspective or mood. Morals can’t be subject to the whims of emotions and justice should not be a synonym of revenge. If we choose to ignore these truths than we do not deserve to call ourselves civilized.
This has nothing to do with defending the actions of those who do violent things. The matter here is how any society can reasonably allow their practice of law to condemn violence with violence. Should we respond to evil with fear and hate? Is that not exactly the pool which spawned the evil in the first place?
There is no moral high ground to a system which takes as its matter of course the disposal of human life. Any life, no matter how it is spent, has to be sacred or all lives are cheapened by its loss. In order to be civilized we have to place our laws above anger, distilling them, purifying them with reason.
Death adds to death, nothing is returned, nothing is gained. Where is the justice in the perpetuation of violence?