The U.S. has less than 5% of the world’s population, yet we have a quarter of the world’s prisoners. Since the declaration of the “War on Drugs” in the 1970s, the U.S. prison population has more than quadrupled. More than 1.5 million Americans are now arrested each year for nonviolent drug offenses, and more than 500,000 of them are imprisoned.

To date, the War on Drugs has killed more than 30,000 Mexicans, made our borders less safe, ruined the lives of millions of American families, wasted hundreds of billions of dollars of taxpayer money, and created the world’s largest prison population. The marijuana prohibition alone costs (by one estimate) more than $40 billion per year—yet it hasn’t achieved its stated goals of reducing marijuana use. Instead, it has created a black market that has turned the pot trade into a lucrative, tax-free industry dominated by organized crime (especially in Mexico, where half the trade is in marijuana) and plagued by the dangers of impure, unregulated drugs. And it stuffs our crowded, enormously expensive prisons with nonviolent pot offenders that don’t belong there.

Since 1990, the U.S. has arrested and prosecuted more than 10 million people, disproportionately African-American, for smoking pot in private—something that brings happiness to many that use it, and causes no harm to those that do not. Yes, it is possible to smoke too much pot, and there can be adverse health consequences of doing so. But those consequences are less than what can result from using too much alcohol, tobacco, junk food, or many over-the-counter medications. Smoking pot is a personal choice that more than four in 10 Americans have made, including the past three presidents, and while it may be a public health issue of interest, it is not a crime against society or against another citizen.

Throwing nonviolent drug offenders in prison puts them in a place where they often can’t easily get treatment for addiction. It crowds out many murderers, rapists, and thieves who do deserve to be there. It numbs society to the seriousness of violence by implying that drug use is just as bad. It undermines imprisonment’s effectiveness as a deterrent to violent crime by cheapening the punishment, turning it into something commonplace. And it blurs the distinctions between moral innocence and moral culpability.

The effects of imprisonment on individuals are far-reaching. Taking people out of society and the workforce ruins not just their own lives, but also the lives of the people that care for them, the people for whom they care, the people whose livelihoods depend on their own. When we use the state’s power of violence to break apart families, to separate husbands from wives, sons from daughters, lovers from lovers, friends from friends, when we replace nature’s most fundamental bonds with gun towers and concrete, we create wounds that take far longer to heal than the inmates’ sentences. The state that uses its power of violence to wound citizens that do not wound others, the state that takes children from their parents when neither poses a threat to the other or to society, has breached its social contract with those that have honored it. The state that harms the harmless is a failed state.

Prop 19 is not a perfect law, and it doesn’t have to be. If it passes, it will quickly change and evolve. What really matters is the message that passing Prop 19 will send: that we need to have a new conversation about drug policy in America. Passing Prop 19 will send our lawmakers, the Obama administration, and the rest of the world the message that American taxpayers are sick of paying tens of billions of dollars every year to throw nonviolent pot smokers in prison, sick of subsidizing criminal gangs by rewarding their activities with a black-market premium, and sick of treating drug addicts—the sick, the tired, the poor, huddled masses, the people who need society’s help most—with violence instead of compassion. It will tell them that we demand an end to the failed War on Drugs, an end to the murders in Mexico, an end to the most expensive waste of law enforcement resources in human history, and a new approach to drug policy and in America and the rest of the world.

Blaming a classifieds web site for the actions of an alleged murderer is almost as absurd as blaming high-school pot smokers for September 11. Nonetheless, Craigslist has decided to remove (or at least rename) the “erotic services” category of the site. This from the New York Times:

“Andrew M. Cuomo, New York’s attorney general, said his office had recently notified Craigslist about an impending prostitution case that involved the erotic services category.

‘Rather than work with this office to prevent further abuses, in the middle of the night, Craigslist took unilateral action which we suspect will prove to be half-baked,’ Mr. Cuomo said in a statement.”

Putting aside the obvious hypocrisy of this particular office’s crackdown on this particular brand of consensual human behavior—and putting aside the disturbing implication that our state’s top law enforcement officer does not subscribe to the principle of innocent until proven guilty—just why is prostitution illegal, anyway?

Prostitution will always be a profession, and it may always be a profession more risky than most. But in justifying the current policy, most prostitution prohibitionists make the same type of correlation-causation mistake that the drug prohibitionists make: they assume that the ills that sometimes surround the culture of prostitution—the pimps, the STDs, the robberies, the poor working conditions, and so on—stem naturally from the activity itself.

Yet there is better evidence that the organized crime, violence, and exploitative labor structures are drawn to the industry precisely because it is illegal—and thus outside the bounds of employment law, taxation, legal remedies for fraud, and other forms of regulation.

It’s the same fundamental correlation-causation mistake that’s made again and again by the White House Office of Drug Control Policy and other War on Drugs apologists: the failure to recognize that criminal behavior often arises from black markets just because they’re black markets, not because of what’s being bought, sold, or consumed.

Even the prohibitionist op-ed contributors to the New York Times, in a piece responding to the Eliot Spitzer controversy, can’t avoid making this basic mistake:

“Whose theory is it that prostitution is victimless?…The Emperor’s Club presented itself as an elite escort service. But aside from charging more, it worked like any other prostitution business. The pimps took their 50 percent cut. The Emperor’s Club often required that the women provide sex twice an hour. One woman who was wiretapped indicated that she couldn’t handle that pressure…The transport of women for prostitution was masked by its description as ‘travel dates.’”

Do these authors really think that these working conditions would still be acceptable at brothels if the businesses were regulated under US labor law?

Now, I don’t mean to suggest that the legalization, taxation, and regulation of prostitution—as has been done in Canada and Britain, among many other countries—would change the fact that when sex is sold, the transaction is usually of a certain sadness. In regimes where prostitution is legal and conditions are thus better for women—protection is enforced, wages and benefits guaranteed, and so on—the sadder party would often seem to be the man: he’s just paid hundreds of dollars for a woman to pretend she likes him for an hour.

On the other hand, anyone who assumes that the relationship between prostitute and client is never one of cordiality and good humor probably hasn’t spent much time talking to prostitutes or clients.

The anthropologist Patty Kelly has done so; she spent a year living in a Mexican brothel and studying the industry, and reports in an LA Times Op-Ed (written in the wake of the Spitzer revelation) that, in one of law enforcement’s more spectacular wastes of resources, more than 80,000 people per year are arrested for prostitution-related offenses. Ms. Kelly suggests an alternative solution:

“New Zealand’s 2003 Prostitution Reform Act is perhaps the most progressive response to the complex issue of prostitution. The act not only decriminalizes the practice but seeks to ‘safeguard the human rights of sex workers and protects them from exploitation, promotes the welfare and occupational health and safety of sex workers, is conducive to public health, [and] prohibits the use in prostitution of persons under 18 years of age.’ Furthermore, clients, sex workers and brothel owners bear equal responsibility for minimizing the risks of STD transmission. In 2005, a client was convicted of violating the act by slipping his condom off during sex.”

Imagine that.

So why isn’t US policy informed by the lessons of Prohibition?

One theory is that while lawmakers do sometimes seem to learn from our country’s mistakes, actually drawing analogies from those mistakes is a more elusive feat—as it is for law enforcement agencies, whose extraordinary leeway in choosing what and what not to pursue gives them a power to shape de facto law more than most citizens recognize.

That is, Mr. Cuomo is actively choosing to spend his time this way.

But there’s another, more intellectually plausible, explanation for why this is allowed to go on. I still remember, from law school, the famous “dwarf-tossing” debate that stood for the question of whether any consensual behavior between adults should ever be criminal. Those who believe it should tend to rely on the position that the criminal law, beyond merely creating a system of incentives, can also have a so-called “expressive” nature—society’s expression of a norm (in this case a behavior—the sale of sex—of which it disapproves) by codifying that norm in the criminal law.

But even if expressive laws are sometimes justified, they should not be imposed in cases that would result in obviously harmful human outcomes like the spread of STDs, violent robberies, the exploitation of women, or the vast waste of Mr. Cuomo’s resources on the victims of these crimes instead of their perpetrators.

The US prohibition on prostitution is no more justifiable than—and, in fact, strikingly similar to—the Catholic church’s prohibition on the use of condoms. When lawmakers, whatever their honest “expressive” intentions, maintain a public policy that is acknowledged to bring about disease and violence, they are willfully putting their own constituents in harm’s way.