When I arrived in Portland last month, the first thing I wanted to do was buy a bike and get around the way the locals do. Since I wouldn’t be in town for too long, and it wasn’t clear that I’d be able to take the bike with me when I left, I wanted something extremely cheap.

There were bike shops on every other corner in Southeast Portland, the sort of Brooklyn-ish neighborhood where I was staying. I walked into what looked like the grungiest of them—a store that sold mostly used bikes. There was one employee, and he was heavily tattooed and seemed pretty cool. I completely leveled with him: I didn’t know anything about bikes, really; I could barely change a tire; I was only going to be in town for a little while, and I wondered if he had something cheap that I could use for puttering around town.

I know this is sort of quaint, but the last time I bought a bike, I think I spent $35, and it wasn’t hot. It was a road bike; it had 18 speeds, I think; it squeaked; and it served my needs (biking from my house to school every day) perfectly well. (The bike later died a peaceful death at Burning Man, but that was due to maltreatment, not poor quality.) I was looking for something like that.

The guy in the store asked me how much I wanted to spend.

I sort of stuttered my way and ultimately refused to answer the question because I was embarrassed to say something like “less than a hundred dollars,” for fear of coming off like Borat inspecting the Hummer before buying the ice-cream truck.

Yeah, the bike guy answered, he had something super-cheap for me, an old road bike that they’d fixed up. It wasn’t exactly my size, but it would do. It was a 1991 model, a Trek, I think; it was in good working condition, it had some newer components, and it came with a warranty. I could have it, he said, for $475.

So I went to another store. Same deal, more or less. There was one bike for $275, but it was a girl’s Raleigh from the 1960s with a wicker basket.

I started looking around the Web. At the down-to-earth-sounding Recyclery, another Portland used bike shop—and probably a great one—there are currently 59 used bikes on offer. But 34 of them cost more than $1,000, only eight are priced under $500, and there are none under $300. Even to rent a bike for one week from the Recyclery costs $175—more than I paid for my weekly rental car the previous time I was in Portland.

At Portland’s Costco, meanwhile—on the outskirts of the city—you can buy a brand-new Schwinn Midtown city bike with Shimano shifters for two hundred something dollars. But, according to the clerk there, those Schwinns aren’t moving.

I don’t doubt that the Schwinn Midtown is a far inferior bike, from the point of view of a bike connoisseur, to whatever’s being sold used in Portland. But you’ve got to love a city whose citizens put a set of moral/aesthetic principles—whether it’s riding a bike with proper disc brakes or refusing to support the Big Box stores—this far above their own financial well-being. And although every city has its bike aficionados, I think that in Portland, most people just buy rebuilt bikes locally because it feels right to do so, not because all these everyday bike riders can really tell the difference between Shimano TX-30 derailleurs and M-970 XTRs.

Still, what’s up with this bike micro-inflation? Why does there seem to be no market in Portland for used bikes that are actually cheap? Portland is otherwise a pretty cheap city. Beer is cheap. Used clothing is cheap. By major urban standards, housing is cheap, too, unless you compare it to the strip-mall-type cities. And certainly there are plenty of people in town who can’t afford to spend $475—never mind $1,000—on a bike.

I asked a few people in town about this, and got some general sense of agreement and common frustration: cheap bikes were impossible to find around here. The word on the street was that so many people were selling their cars (or taking their cars off the road) and using bikes to commute to work that there just weren’t enough bikes to go around. I also heard about a guy who was actually in the business of bicycle arbitrage—he would immediately snap up the few cheap bikes that would come up on Craigslist, fix them up a bit, put them back up on Craigslist, and make a good profit.

So I started looking at Craigslist—not just in Portland, but in other cities too, and not just at bike prices, but also at car and truck prices. I looked at a wide range of midsized-to-large cities that I thought represented a diversity of urban layouts, bike prevalence, wealth, and so on: Austin, Miami, New York City, Phoenix, Portland, San Francisco, and Seattle.

From each of these cities I collected an extremely basic data set: the asking prices for the 50 most recent cars/trucks and bikes advertised. I excluded children’s bikes, frame-only bikes, and non-working bikes; I excluded non-working cars and cars that were being sold for parts. I also excluded obvious dealer spam from each. Then, I looked at the medians. Here’s what happened:

Median price, first 50 items for sale on Craigslist, 8pm PDT, 8/13/09

I didn’t run any serious statistical tests on the data set. This is because there are a few fundamental problems—the largest being that we’re not comparing apples to apples in terms of what’s being sold. That is, we don’t know if the same types of bikes are being sold for more in Seattle than in Phoenix, or if there are different types of bikes being sold in the two markets. The ads also change so frequently that replicating these results might be difficult; and 50 data points might be too small a sample.

Still, whether it’s over/underpricing or just selective selling, what struck me about this informal little analysis was that not one city fell out of line in the inverse order. Where cars were selling for the most, bikes were selling for the least; where cars were selling for the least, bikes were selling for the most; and so on, inversely, in between.

So, it looks like even though there are tons of bikes and bike shops in Portland, there still aren’t enough sellers in town to satisfy the strong demand in this biker’s paradise. Perhaps, in the long run, when enough arbitrageurs start shuffling bikes around the country (and enough arbitrageurs start underpricing each other to drive down their margins), more cheap used bikes will become available in the bike-friendly cities.

In the meantime, if you’re a Portland or Seattle resident thinking of selling your car and going green, maybe you should drive down to Phoenix and ride a bike back. You’d leverage both sides of the inverse relationship—plus there’d be some beautiful scenery along the way.

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.