It seems there are questions with answers that should be perfectly clear. For instance, is it permissible to kill someone? The immediate, visceral response is a firm "no." Yet, if we linger on the question, the edges of that certainty begin to blur. What if you are attacked and must defend your own life? What if a person, in unbearable suffering, begs for release? What if you are faced with a terrible choice, like the one that haunts heroes in our stories: kill one monstrous person to save hundreds of innocent lives? Suddenly, the obvious is no longer so simple.

We are raised with the deep-seated understanding that murder is a profound crime, but this has not been a universal truth across all human societies. In some eras, taking a life was not only accepted but even encouraged. For the warriors of Genghis Khan, a man’s worth was often measured by the number of enemies he had slain.

A Taboo Forged in Survival

From the moment early humans fashioned the first tools, any object could potentially become a weapon. But what led us to turn these weapons on our own kind? The zoopsychologist Konrad Lorenz offered a compelling explanation. He argued that natural predators—animals equipped with fangs, claws, and overwhelming strength—evolved an instinctual check that prevents them from killing members of their own species during conflicts. This mechanism is essential for self-preservation; a species that constantly kills its own in disputes over dominance or territory would quickly vanish. Among wolves, for example, a fight for dominance ends when the weaker animal submits, and both live to see another day.

Humans, by contrast, are not natural predators in the same way. Killing another person with our bare hands is a difficult, intimate, and gruesome act. Because of this physical challenge, Lorenz theorized, we never developed that same powerful, instinctual brake on intraspecific aggression. It was assumed our physical limitations were enough. Then, we invented weapons. A spear, a rock, a blade—these tools bypassed our physical inadequacy and made killing efficient and impersonal. Without a natural mechanism to hold us back, what was to stop us from wiping ourselves out?

Survival. We developed a social one: the taboo. The prohibition against killing was born not from a sense that every individual life was sacred, but from the pragmatic need to preserve the community. The tribe, the collective, was what mattered most. It was this focus on the group that led to a strange paradox: to protect the community, it was sometimes deemed necessary to kill individuals who threatened it from within. This was the charge leveled against Socrates in ancient Athens. His progressive views and questioning of the gods were seen as a poison corrupting the youth, a threat to the future of their society. The verdict was death.

The Soul's Burden: Philosophical and Spiritual Prohibitions

The death of Socrates and the eventual rise of Christianity in Europe marked a profound shift in this thinking, solidifying the Sixth Commandment: "Thou shalt not kill." In the Christian worldview, every single life is precious to God. Because God is the origin of all life, to unlawfully take a life is to trespass on the divine. It is a sin that damages not only the victim but the perpetrator as well.

The English preacher John Donne eloquently captured this sense of interconnectedness, stating that "any man's death diminishes me, because I am involved in mankind." In this light, murder is a self-inflicted wound. The philosopher Immanuel Kant echoed this sentiment from a secular perspective. He argued through his categorical imperative that when a person acts, they are willing that act to be a universal law. Therefore, when you steal from another, you consent to being stolen from. When you take the life of another, you are, in a philosophical sense, taking your own.

This principle of universal love and non-violence reached a zenith with thinkers like Leo Tolstoy, who believed that evil could never be fought with its own tools. Citing the Sermon on the Mount—"Do not resist an evil person. If anyone slaps you on the right cheek, turn to them the other cheek also"—he advocated for a radical commitment to love in the face of violence. But this raises a troubling question: in a world where evil exists, would such a principle lead to the triumph of good, or its annihilation?

The Cold Arithmetic of Morality

Not all philosophers agree that violence is never justified. Gottfried Leibniz, who famously argued that we live in "the best of all possible worlds," saw a murderer as someone who disrupts the fundamental harmony of existence. For him, retribution was not just satisfying; it was a necessary act to restore that cosmic balance. Kant, for all his focus on the value of life, shared this view when it came to justice. He believed that if a person commits murder, they must forfeit their own life. This, in his mind, was the only way to uphold a society founded on law and reason.

But does every killer deserve to die? The question becomes intensely complicated when we introduce variables. This is the moral landscape of the famous "trolley problem," formulated by Philippa Foot. A runaway trolley is about to kill five people tied to the track. You have the power to pull a lever and divert it to another track, where it will kill only one person. Is it justifiable to actively cause the death of one to save five?

This is the dilemma that Batman faces with the Joker. By killing the Joker, a single person, he could save countless future victims. By refusing, he upholds his own moral code, but many more will die. From a Nietzschean perspective, Batman chooses a "slave morality," adhering to a code that society has imposed upon him. In contrast, a character like Thanos from modern cinema chooses the "master morality." He takes it upon himself to change the world by his own will, sacrificing half of all life, including his beloved daughter, for what he believes is the greater good. He seizes the responsibility to decide.

The State's Prerogative: Who Decides Who Lives and Dies?

In the societies we live in today, who has the right to make these choices? The state. Through the social contract, we relinquish a portion of our individual freedom in exchange for collective security. In return, the state holds a monopoly on legitimate violence. It is the state that, through its courts and laws, decides if an act was justifiable self-defense or murder. It weighs in on the legality of euthanasia.

And in many places, it is the state that holds the ultimate power of life and death through capital punishment. The death penalty remains legal in over 80 countries, representing a form of conditionally legal, state-sanctioned killing. For many, this feels just. Some argue from a place of practicality—why should taxpayer money be spent to sustain the life of a convicted murderer? Others see it as the only true justice for the most heinous of crimes.

However, the arguments against it are formidable. There is the irreversible tragedy of executing an innocent person due to a flawed investigation. There is the potential for repressive regimes to use it as a tool to eliminate political opponents. And as the dissident Andrei Sakharov pointed out, there is the moral injury to society itself. Who, he asked, is supposed to carry out these sentences? What does it do to the psyche of a person whose job it is to kill on behalf of the state? Capital punishment introduces a glaring contradiction into our legal system: we forbid killing, and so we kill the killer.

We cannot bring the dead back to life. Faced with that irreversible fact, we are left standing at a moral crossroads. The questions remain, echoing in our courts, our stories, and our own consciences. Can we ever truly justify taking a life, or is it a line that, once crossed, diminishes us all?

References

• Lorenz, K. (1966). On Aggression. Harcourt, Brace & World.

  This foundational work by the Nobel Prize-winning ethologist explores the biological roots of aggression. Chapter 11, "The Bond," is particularly relevant, as it discusses the social instincts and inhibitory mechanisms that prevent animals within a species from killing each other, and how these mechanisms may be weaker or function differently in humans, a central point in the article's opening argument.

• Foot, P. (1967). The Problem of Abortion and the Doctrine of the Double Effect. Oxford Review, 5, 5–15.

  This seminal essay is where philosopher Philippa Foot first introduced the thought experiment that would become known as the "trolley problem." The entire paper is essential for understanding the ethical conflict between direct harm and allowing harm to occur, which forms the basis for the article's discussion on utilitarian choices versus deontological rules.

• Kant, I. (1797). The Metaphysics of Morals.

  In Part One of this work, "The Doctrine of Right," Kant lays out his theory of justice and punishment. Specifically, in section 49 on "The Right to Punish," he argues for the jus talionis (the law of retribution). He makes his famous case that death is the only penalty proportionate to the crime of murder, providing the philosophical backbone for the retributive arguments discussed in the article.