In "Utopia", Sir Thomas More wrote that the government should stop focusing on enforcing harsh penalties for theft, and instead focus on eliminating the policies that led to the impoverishment of the tenant farmers (namely, encroaching on and fencing-off their lands, effectively forcing them to compete for labor in the city centers to survive).
Abbie Hoffman wrote that the decades-long prison penalties for violating anti-marijuana laws made it so that young people may feel pressure to commit acts of violence (including, potentially, murder) against witnesses in order to prevent being punished for the original crime.
Why do people turn to theft, drugs, and violence? They perceive that they have few other options. They harm themselves, others, and others' property, often as a way to feel in-control; while society has conditioned the set of legitimate alternative courses of action available to them.
It should make sense, then, that several of the last few famous American mass shooters were on prescription anti-depression and anti-schizophrenia medications. Depression and schizophrenia are over-diagnosed, and the medications prescribed to treat them often have suicidal thoughts as side effects.
We must begin viewing many of these shootings as symptoms of the ills of society, not simply as ills. Saying that a mass shooter was "deranged" is a cop-out. But calling for "free" psychiatric care for all Americans (as a preventive measure) is an expensive proposition that diminishes the value of the labor of the people who perform psychiatric evaluations for a living.
Capital punishment (execution) is not an effective deterrent for murder; like the marijuana example, it only leads to (and, in the criminal mind, excuses) further violence. But prison - with its routine beatings and rapes (corporal punishment, whether sanctioned or overlooked) - is no creative or effective way to humanize the criminal justice system.
In some non-industrialized societies [including the Babemba tribe of Africa], when a person commits a crime, it is seen as a cry for help, and the village comes together to praise the criminal, and tell him about all the good things he has done in the past, in order to convince him that he is a good person (no deterrence necessary). Similarly, Socrates suggested that as "punishment" for corrupting the youth of Athens he should not be sentenced to death but instead given free food for life.
The trial of Socrates undoubtedly led his student Plato (who wrote, "[g]ood people don't need laws to tell them to act responsibly, and bad people will find a way around the laws") to wonder whether justice is truly good or instead simply a necessary evil. It is an appropriate question, especially given that today some homeless commit acts of petty theft so that they will be arrested and taken to jail, thus ensuring them shelter for the night, and possibly also a meal or two.
It should seem obvious by now that once a man has killed, he is willing to eliminate witnesses without blinking an eye. So too police, and whatever non-witness innocent bystanders happen to be between him and his getaway car. Thus, the fear of being confronted with deadly force is not an effective deterrent for these people who have little or nothing to lose.
But what good, exactly, would result from the legalization of murder? In all likelihood, nothing. But what good has resulted from its decriminalization (i.e., reduced penalties, and augmented rights of the accused)? It depends on whether you ask a civil-libertarian or someone who thinks society "coddles" criminals and the disadvantaged.
So why, then, even bring up the idea of legalizing murder (that is, repealing laws against murder, and eliminating sentencing guidelines for it)? We may remember from the First Book of Timothy "...law is made not for the righteous but for lawbreakers and rebels...". Just as "when guns are outlawed, only outlaws will have guns", when murder is outlawed, only outlaws will commit murder.
Actions are not immoral because they are illegal, but illegal because they are immoral. Those who believe that murder is wrong will not commit murder, and nothing will stop those who do not care whether murder is wrong from committing it.
Nothing, of course, except threats by individuals (and threatening by the State, called "laws") that such actions will be met with violent retribution. And, naturally, in the absence of Statism, the same set of threats would have the same potential to prevent aggression and enact retribution against its victims.
In addressing the complaints of voters upset by the legalization of gay marriage, stand-up comic Daniel Tosh remarked that the fact that gay marriage is legal doesn't mean that people who participate in homosexual civil unions are not going to go to Hell, saying "Just because the state says it's legal, it's not like God's gonna let 'em into Heaven."
Maybe if legalizing murder doesn't work, we can always replace those "gun-free zone" signs in schools with "murder-free zone" signs.