Human life is sacred, no exceptions.
Of course, few people would attribute absolutely no value to human life, but, many people do possess certain judgements and opinions that are inconsistent with the absolute value of human life.
What do I mean by that?
Think of somebody in your day-to-day life who you hate, who drives you up the wall. Would you be glad if that person were to suddenly die? To most people, of course, the obvious answer would be “no”. And why is the answer no? Because human life has an innate value that would render its loss a sad event, or a major injustice in the event of a murder.
However, people often tend to perceive exceptions to this principle of moral law; it is an unfortunately common perception that gross violations of moral law can make a person deserve death. Those who believe in the death penalty would think, for instance, that electrocuting a murderer is “justice served”. Assuming that the criminal in question is within a secure justice system and could otherwise be confined to a jail cell without a reasonable fear of his escape, what kind of justice is that? The proper function of a justice system is to prevent and deter crime; a culprit of such a high crime, if imprisoned for life, is very unlikely to commit further offenses. The will to kill him, in this case, stems solely from emotion, the desire for harsh retaliation.
The problem with believing in “killing for justice” is that it represents a reduced sense of value for human life. Killing another human being is only justified in a select few situations, in which the direct culprit of such high and infamous crimes as mentioned earlier represents such an immediate, likely, and direct threat to the lives of others that he/she cannot be securely imprisoned. If an intruder with a firearm were to shoot you, for instance, shooting him in self-defense wouldn’t be a problem. Or, say that an army unit has captured a leader of a terrorist organization responsible for the deaths of thousands, but his allies (hypothetically speaking) are approaching in large numbers to retrieve him. In the context of the immediacy of the situation, that the soldiers would not likely be able to bring the culprit to trial, he is directly dangerous enough to kill. Human life may only be sacrificed in this manner if it is absolutely necessary.
On that note, it is also wrong to wish for the death of any other person. Even for the homicidal home invader described in the first scenario, potentially fatal force should only be used as a last resort; to believe that a person deserved death anyways is to imply that his/her actions have destroyed the value of his/her life, and it can be taken away. No. Human life is sacred.