Following in the footsteps of so many people before him, Juan Pimentel saw opportunity in restrictive laws. It's an old story; government officials tell people they can't have what they want, and that prohibition creates a lucrative business opportunity for anybody willing to break the law to keep buyers happy. But when Pimentel was pulled over two weeks ago north of Tucson, Arizona with 150 pounds of forbidden cocaine destined for Chicago, there was something a little special about him: he was a U.S. Border Patrol agent—one of the people hired and trusted to enforce government officials' will.

Sarah Furay's case is a little different, since she had no badge in her wallet when she was busted last month in College Station, Texas with commercial quantities of cocaine, marijuana, Ecstasy, psychedelics, hash oil, and hydrocodone (one-stop shopping, indeed). But she is the daughter of Bill Furay, a Drug Enforcement Administration official with the U.S. embassy in Panama and the former head of the DEA office in Galveston, Texas. No doubt, she's had ample opportunity to see the potential for profit in the laws her dear old dad enforces.

Worries about enforcers succumbing to the temptations of the things they're supposed to control are so old that they're most famously captured by a saying in a language that's been effectively dead for centuries: Quis custodiet ipsos custodes? Who watches the watchmen? Maybe the answer is the bartender. More recently than the long-gone days of ancient Rome, my great-grandfather served drinks to the then-New York City police commissioner at his speakeasy in the Bronx. My understanding is that, at the very least, the Prohibition-era top cop didn't have to worry about paying his tab.

Legal assaults on the relationships among willing buyers and sellers of goods and services that government officials don't like face special challenges. "Drug arrests and prosecutions are exceedingly difficult, owing to the absence of complaining victims and witnesses," pointed out a 1989 National Institute of Justice report on the challenges of enforcing laws against disfavored intoxicants. With no outraged victims to press charges, enforcers inevitably resort to underhanded tactics – but that raises all sorts of new dangers. "Informants and undercover operations–so essential to effective drug enforcement–inevitably draw police officers into close, potentially corrupting relationships with the offenders they are pledged to control," the report continued.

"Potentially corrupting?" How could such relationships not be potentially corrupting when upwards of $100 billion slosh through the black market for cocaine, marijuana, methamphetamine, and heroin every year, as estimated for the White House Office of National Drug Control Policy by the RAND Corporation?

Cops, then, face a choice between enforcing restrictive laws on willing participants in banned markets—people who don't want or need any such "help" and deeply resent the imposition—or else trying to get a piece of that $100 billion for themselves.

No wonder some of them choose the path selected by Pimentel. Or that preferred by King County Sheriff's Deputy Mitchell Wright, who started as a member of an anti-drug task force and ended up reselling drugs seized as evidence. And then there are the six Philadelphia narcotics cops who stole over $500,000 from drug suspects. And the eight New York City police officers busted for dealing in tightly controlled (in New York) guns and cigarettes.

Yes, police can be corrupted by participants in all sorts of crimes—a bribe to look the other way is an old tradition. But prohibition-induced corruption really is a special variety, the Government Accountability Office (GAO) concluded in a 1998 study:

"Enforcement of laws against all forms of vice (e.g., gambling, prostitution, and drugs) reportedly afford opportunities for police corruption. However, drug enforcement often exposes police officers to large amounts of cash and drugs held by individuals who are not likely to complain about illegal police behavior. Recent newspaper accounts, commission reports, academic studies, and other literature we reviewed suggest that today there are more opportunities than in the past for drug-related police corruption."

The GAO also concluded that, while most crooked cops traditionally were individuals taking a few bucks to look the other way, the prohibition-related variety typically involved groups of officers "actively committing crimes."

Probably the most famous example of exactly that is in Mexico, where special forces soldiers deserted from the army and established the drug cartel known as Los Zetas. It doesn't get more "actively committing crimes" than that.

Not even the most controlled environments, such as prisons, can change the incentives for corruption inherent in prohibitions. That's because those exercising the control have endless opportunities for turning a profit by violating the rules. When it comes to smuggling illicit items such as drugs, cigarettes and cell phones behind bars, "Often the people doing the smuggling are guards or other corrections employees," reports Matt Clarke for Prison Legal News.

Not that politicians seem prone to learn any lessons from the corrupting history of prohibitions. President Obama has made a hobby of following up news reports of murderous crimes with calls for new restrictions on firearms—most recently, just this past Sunday. Let's see, tighten restrictions on valuable goods that people want to own (record sales are recorded every time the president opens his mouth) and are willing to pay good money to purchase. What could go wrong?

Then again, maybe the outgoing chief executive is looking for post-presidential opportunities and intrigued by the example of California State Sen. Leland Yee, a gun control advocate who ran weapons on the side. It's not as if government officials haven't had plenty of experience illegally trafficking in firearms in recent years, as the gunwalking scandals so aptly demonstrated.

As Pimentel and Furay and so many law enforcers have shown us over the years, prohibitions are just good business and they have plenty of experience exploiting them for profit.