Marijuana became functionally illegal in the United States in 1937, and by the time we reach the century mark on this prohibition, it will likely be over. I argued four years ago that legal weed is all but a done deal; it is even easier to be confident in that claim today, with as many as 40 states poised to have some sort of legalization measure on the books by the end of 2020.

But it would be absurd to look at the last three decades' lurch of public opinion on marijuana and conclude Americans have developed a philosophical opposition to prohibition. While the prospect of legalizing weed no longer shocks — in my lifetime, support has gone from 16 percent to 67 percent — we are still profoundly indecisive on the principle of the thing: The smoking age was raised from 18 to 21 in December. The FDA just banned most vaping flavors for individual e-cigarettes. And a recent piece at The Atlantic wondered why the United States lacks a modern anti-alcohol movement.

This is a strange incoherence — a cognitive dissonance — which suggests we never rightly extrapolated the lessons of the Prohibition era. We can recite them well enough, explaining that, though well-intended, the policy's consequences were disastrous. A black market sprung up which proved dangerous in its methods and products alike. Meanwhile, in the legal economy, thousands of jobs were lost in liquor, transportation, and amusement industries. Drug use rose; tax revenues fell and government spending increased; corruption spiked; violent and property crime flared while police were tasked with Prohibition enforcement. And after an initial decline, alcohol consumption rose throughout the Prohibition years, nearly reaching pre-Prohibition levels by its end.

We all know capital-P Prohibition failed. So why haven't we once and for all rejected other prohibitionary policies, like the drug war and harsher tobacco regulations?

"A lot of it has to do with some embedded racism and just basic moralizing," Dr. Jeffrey A. Singer, a senior health policy fellow at the Cato Institute, told The Week. Few support reviving Prohibition-style restrictions on alcohol because of its familiarity, said Singer, who is also a practicing physician. Most of us have consumed alcohol and know how to do so safely. Though some deal with alcoholism or otherwise have an unhealthy relationship with drinking, alcohol itself isn't generally stigmatized because of its widespread use.

With other substances, Singer continued, the cultural context is different. "People have come to associate those substances — at least, originally — with marginalized populations. Not 'us,' you know, but 'them,'" he said. "So, for example, in the early days, when cannabis prohibition started in the late 1930s, it was explicitly either migrant Mexican farm workers or African-American jazz musicians. And in 1930s, these were people who were not 'us,' these were the outsiders, so it was easy to kind of tap into people's prejudices."

In the years since, marijuana use has been normalized for the white majority in a way approaching alcohol's societal status — and that, Singer said, helps explain the changing legal climate. But while weed is becoming a substance "we" use, tobacco's reputation has taken a hit. Since the early 1970s, public health campaigns have made smoking socially undesirable, something nice, white, middle class people don't do. The prohibitionary policies have duly followed, even for e-cigarettes, which are substantially less harmful than smoke-based tobacco products. (Most of the few dozen deaths connected to vape use — and compare that to hundreds of thousands of smoking-related deaths annually — involve black-market modifications which could be made safer absent a ban.)

The substances are different, but the social dynamic is the same. When thinking about alcohol and substances, like marijuana, which gain a similarly wide cultural acceptance, Americans understand why prohibition is ineffective and indefensibly inhumane. But when "we" are asked to think the same way about substances associated with people unlike ourselves — harder drugs and, increasingly, tobacco — our logical and historical reasoning goes up in smoke.

People "do understand it conceptually," Singer mused, "but I think their emotions get in the way of allowing them to connect the dots." One possible aid in making those links, he proposed, is exposure to harm reduction options which also make sense from moral and public health standpoints. That could look like witnessing the effects of decriminalization of all drugs in Portugal, for instance, or having a methadone user as a coworker. Advocacy for medical marijuana helped normalize recreational legalization, Singer said, as Americans observed ordinary family members using pot for medical purposes without the Reefer Madness-type results they'd been told to expect.

That sort of evolution, that expansion of "us," would be better than nothing. But better still would be the development of a deeper coherence on prohibition, an understanding that it's just as bad for other people as it is for us.