While Australia no longer has the death penalty, it is worth reminding ourselves why our state does not kill its own citizens, however vicious they might be.

Take a recent case in the UK. Two inmates from a maximum security prison were convicted of murdering another inmate. Gary Smith and Lee Newell, both incarcerated for murder, killed child murderer Subhan Anwar.

This was not a rage killing but an argument that turned physical. Armed with "shanks", the killers calmly followed Anwar into his cell, locked the door and blocked the peephole. They then tied up their victim's legs, and strangled him with his own tracksuit bottoms.

Why was Anwar killed? During Smith and Newell's trial, the victim's own crimes were noted: he had murdered his partner's two-year-old child, and there was a "code" among many prisoners. Perpetrators of crimes against children are often victims of abuse in jail.

This makes a certain primal sense as the details of Anwar's crime prompt horror and fury. All the child's limbs were fractured and she died after "fatty deposits from her broken thigh bones entered her bloodstream". Having read this, I must be frank: execution has a certain visceral appeal.

But when asked why they killed Anwar, one of the killers told guards: "I'm bored, it was something to do." This might have been bluff and bluster - the facade of blase hardness. But Newell was consistently unclear about his motives. "I don't know," he told a negotiator. "I wish I knew myself." If true, this was more complicated than righteous revenge. Anwar's crime did not necessitate his death, it merely excused it. This was not retribution, but rather entertainment with a ''legitimate'' target.

Still, some might argue that there's a certain justice to the crime. Two convicted murderers executed a convicted murderer. The perpetrators will be jailed for life. Three killers are now removed from society - one completely and two all-but. And neither private citizens, nor the state, had to get their hands dirty, so to speak. All the crimes were committed by criminals.

Given the suffering of these men's victims, is this not the best possible outcome?

At first blush, this seems so. Apart from the families and friends of those involved, no one will weep for Anwar or his murderers.

But the fact that they are jailed introduces another point: Anwar's death is also considered a crime. There is no simple eye-for-an-eye justice here: his life for his victim's. The state treats the premeditated murder of murderers as a crime, worthy of a life sentence, just like any other.

This is another way of saying that Anwar's life has value. It is not simply that Newell and Smith have broken a law and, as such, must be punished. The law exists because we value human life.

And, more important, we place the same value on different lives. Even criminals, deprived of their privileges, are not supposed to be deprived of their existence altogether (in the UK and Australia, at least). This is also why we have protective custody, because the state expends resources protecting criminals from one another, not because they might be innocent but because their lives are valued formally by the state and those who uphold its laws, if not by many individuals.

This is a somewhat Kantian belief: another life is not ours to own, use or discard. Each self is an end in itself, and ethics is meaningless if this is not granted. We treat one another, formally at least, as free agents, not as things to be used and discarded. This does not mean the punitive system is perfect in Australia or the UK, that prisons do not contribute to crime, or cause physical and psychological illness. More generally, it does not mean that our society is always just. Note how we punish asylum seekers to ''send a message'' to smugglers. This is to say nothing of our exploitation of those abroad such as the cheap labour that keeps profits high and holds off overaccumulation.

The point is that we still retain some commitment to the value of life, and our punitive laws, however imperfectly framed and applied, formally reflect this commitment. We uphold these laws so that, when acts of human savagery or callousness occur, the state stops us from responding in kind. In this, the law takes for granted our most basic humanity, but our continual commitment to the law demonstrates it.

Damon Young is a philosopher and author. His latest book, Philosophy in the Garden, was published last year. Twitter: @damonayoung