Prohibitionists were outraged by President Obama's recent observation that marijuana is safer than alcohol—not because it is not true but because it contradicts the central myth underlying public support for the war on drugs. According to that myth, certain psychoactive substances are so dangerous that they cannot be tolerated, and the government has scientifically identified them. In reality, the distinctions drawn by our drug laws are arbitrary, and marijuana is the clearest illustration of that fact.

"As has been well documented," Obama told The New Yorker's David Remnick in an interview published last week, "I smoked pot as a kid, and I view it as a bad habit and a vice, not very different from the cigarettes that I smoked as a young person up through a big chunk of my adult life. I don't think it is more dangerous than alcohol." When Remnick pressed him to say whether marijuana is in fact less dangerous than alcohol, the president said yes, "in terms of its impact on the individual consumer."

Judging from survey data, that is not a very controversial position. According to a recent CNN poll, 87 percent of Americans think marijuana is no more dangerous than alcohol, and 73 percent say it is less dangerous. Yet Obama's statement does seem inconsistent with his administration's stubborn defense of marijuana's placement on Schedule I of the Controlled Substances Act, a category supposedly reserved for drugs with a high abuse potential that have no recognized medical value and cannot be used safely, even under a doctor's supervision.

The administration concedes that chemicals in marijuana have medical utility, but it argues that they should be taken in isolation, not by smoking, vaporizing, or ingesting the plant. The administration also maintains that marijuana's popularity as a recreational intoxicant demonstrates its high potential for abuse—if you define abuse to include all nonmedical use, as the government does.

Both of these claims are debatable, to say the least. But marijuana's Schedule I status seems especially vulnerable when you consider the safety prong. Alcohol, despite its familiar hazards, can be consumed safely, even without medical supervision. If marijuana is less dangerous than alcohol, it necessarily follows that it also can be consumed safely. And if marijuana does not belong on Schedule I, then by definition it should not be banned.

As you might expect, survey data indicate that people who believe marijuana is safer than alcohol are especially likely to support legalization. In a 2012 survey by Public Policy Polling, 92 percent of respondents who strongly agreed that marijuana is safer supported legalization, compared to 24 percent of those who strongly disagreed. Increased understanding of these drugs' relative hazards seems to be one of the main factors driving up support for legalization, which according to several recent polls is now favored by most Americans.

You can see why pot prohibitionists reacted with dismay to Obama's comment—not because it was false but because it was true. As measured by acute toxicity, accident risk, and the long-term health effects of heavy consumption, marijuana is clearly safer than alcohol. That does not mean smoking pot poses no risks, or that drinking is so dangerous no one should ever do it. It simply means that the risks posed by alcohol are, on the whole, bigger than the risks posed by marijuana. So if our drug laws are supposed to be based on a clear-eyed evaluation of relative risks, some adjustment would seem to be in order.

No, no, no, say the prohibitionists. Patrick J. Kennedy, the former Rhode Island congressman who chairs the anti-pot group Project SAM, says, "We take issue with the President's comparisons between marijuana and alcohol." Yet Kennedy does not really explain why. Here is the closest he gets: "Two wrongs don't make a right: just because our already legal drugs may have very dangerous impacts on society it does not mean that other drugs should follow the same path." The first "wrong," according to Kennedy, was repealing alcohol prohibition. Having made that mistake, he says, we should not compound the problem by legalizing another recreational intoxicant, even if it is less hazardous than alcohol.

That argument can be challenged on practical and moral grounds. If marijuana is a substitute for alcohol (as some evidence suggests), legalizing it could lead to a net reduction in drug-related harm. And even if you accept the paternalistic premise of the war on drugs, it does not seem fair to treat suppliers of one drug as criminals while treating suppliers of a more dangerous one as legitimate businessmen.

Yet Kennedy's argument is a rhetorical tour de force compared to the protests lodged by other prohibitionists. Writing in The Washington Times, former Oklahoma congressman Ernest Istook complains that "pro-pot proponents…adopt an extremely narrow definition of marijuana's dangers by [focusing] solely on whether it is 'toxic.'" Istook is alluding to the fact that it is fairly easy to consume a fatal dose of alcohol, while there has never been a documented death from a marijuana overdose. That fact does seem pretty important in evaluating the relative risks of these two drugs, but it is not the only consideration. "Pro-pot proponents" also note that marijuana impairs driving ability less than alcohol does and that heavy drinking causes devastating organ damage unlike anything seen with marijuana.

Istook trots out the old canard that "marijuana smoke has significantly more carcinogens than tobacco smoke," implying that marijuana poses a bigger cancer risk. But the typical pot smoker absorbs much lower doses of combustion products than the typical cigarette smoker does, and the epidemiological evidence linking pot smoking to lung cancer, unlike the evidence linking cigarette smoking to lung cancer, is equivocal. Furthermore, there are other ways to consume cannabis (vaporization and edibles) that do not involve inhaling smoke.

Istook claims "adolescent use of marijuana…causes permanent brain damage"—an unproven assertion based on correlational evidence that does not necessarily indicate a cause-and-effect relationship. Public health officials also warn that adolescent brains may be especially vulnerable to the effects of alcohol. That concern is not usually considered an argument for banning alcohol consumption by adults.

Still not convinced that the president was wrong when he said marijuana is safer than alcohol? He can't be right, Istook says, since "the official National Drug Control Strategy from drug czar R. Gil Kerlikowske lists marijuana as one of the 'four major drugs (cocaine, heroin, marijuana, and methamphetamine).'" There you go: Since marijuana is a popular illegal drug, it cannot possibly be safer than alcohol. Istook closes with a sneer that was already old when he was elected to Congress in 1992. If you disagree with him about marijuana's dangers, he says, you "must be smoking something."

Simply citing risks posed by marijuana, even if they are well established, does not prove it is more dangerous than alcohol—a basic logical point that the president's critics do not seem to understand. "President Obama is surrounded by a myriad of experts who have voiced serious concerns about the harms of marijuana," says the Drug-Free America Foundation, "so either he is seriously ill-informed about the issue or is completely ignoring warnings from his highly esteemed advisors."

Drug warriors also were irked that Obama, rather than reiterating his opposition to marijuana legalization, seemed curious to see how the experiments in Colorado and Washington turn out. Expressing concern about the racially disproportionate impact of pot prohibition, he told Remnick "it's important for [legalization] to go forward because it's important for society not to have a situation in which a large portion of people have at one time or another broken the law and only a select few get punished." A few days later, White House Press Secretary Jay Carney emphasized that "the president's position on these matters hasn't changed" and that "he's not endorsing any specific move by a state." Rather, "he's talking about the issue of disparities in prosecution of our drug laws that an experiment like this may be addressing."

Still, Obama's openness to the possibility that marijuana legalization might be something other than a disaster is too much for those who view the plant as inherently evil. "His laissez-faire attitude about legalization has drug policy and prevention experts scratching their heads in confusion as to why the president will not give clear guidance," complains the Drug-Free America Foundation. "His lack of a formal position on what he is or is not supporting is an irresponsible move for such a person in the most highly regarded position in this country."

The drug warriors' confusion reminds me of that Star Trek episode in which the robed agents of repression who enforce a brutally blissful dictatorship, having been freed from the mind control of the computer that runs their society, wander around crying, "Landru! Guide us!" On the subject of marijuana prohibition, it is long past time we started thinking for ourselves instead of relying on a government that has been lying to us for 77 years.

This article was originally published by Forbes.