A front-page story in yesterday's New York Times notes the divide within the anti-smoking movement on the merits of electronic cigarettes, as exemplified by the split between Boston University public health professor Michael Siegel and his former mentor, Stanton Glantz, director of the University of California at San Francisco's Center for Tobacco Control Research and Education. The Siegel camp sees e-cigarettes, which deliver nicotine without tobacco or smoke, as a promising harm reduction tool, while the Glantz camp sees them as a public health menace. Because health reporter Sabrina Tavernise accurately summarizes the arguments of both sides, it is hard to see how a fair-minded reader could end up agreeing with Glantz. Here are the two main arguments against e-cigarettes:

E-cigarettes will lure teenagers into smoking. Since avoiding that smelly, dirty, and dangerous habit is the main motivation for vaping, this fear seems implausible. Furthermore, there is no evidence that e-cigarettes are serving as a gateway to the conventional kind. In fact, the recent increase in vaping among teenagers has been accompanied by a continued decline in smoking.

Vaping will discourage smokers from quitting by giving them a way to get their nicotine fix when they can't light up. Again, there is no evidence that is actually happening, and the same objection could be raised against nicotine gum, lozenges, or patches.

As Tavernise notes, the "public health" debate about e-cigarettes "comes down to a simple question: Will e-cigarettes cause more or fewer people to smoke?" The testimonials of vapers tell us that e-cigarettes are a viable alternative for many people who would otherwise continue sucking smoke into their lungs. We know those people actually exist. The same cannot be said of smokers who never would have started or who would have quit but for e-cigarettes. Those vaping-enabled smokers may exist only in the imaginations of Glantz and his allies. So if your concern is the net impact on tobacco-related morbidity and mortality, the existing evidence strongly favors e-cigarettes.

Regardless of how that collectivist calculus comes out, the indisputable safety advantages of e-cigarettes would be enough to recommend them as an option for individual smokers. Unlike some of her colleagues, who in the past have implied that the relative hazards of smoking and vaping are a matter of scientific dispute, Tavernise understands the significance of eliminating tobacco and its combustion products:

Public health experts like to say that people smoke for the nicotine but die from the tar. And the reason e-cigarettes have caused such a stir is that they take the deadly tar out of the equation while offering the nicotine fix and the sensation of smoking. For all that is unknown about the new devices—they have been on the American market for only seven years—most researchers agree that puffing on one is far less harmful than smoking a traditional cigarette.

None of the e-cigarette critics quoted by Tavernise disputes that point, and it is hard to imagine how anyone reasonably could (although that does not stop some activists from trying). But the huge difference in risk between vaping and smoking is not enough for Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention. "I think the precautionary principle—better safe than sorry—rules here," he tells the Times. In what sense is it "safe" to prevent smokers from buying a product that could literally save their lives? If the Food and Drug Administration, which is supposed to start regulating e-cigarettes soon, takes its cue from Frieden, the result could be more smoking-related disease and death instead of less. "If we make it too hard for this experiment to continue," says Siegel, "we've wasted an opportunity that could eventually save millions of lives."

Frieden has been known to simply make stuff up in his campaign against vaping, claiming without any evidence that "many kids are starting out with e-cigarettes and then going on to smoke conventional cigarettes." That he is now resorting to the precautionary principle—which my colleague Ron Bailey aptly sums up as "never do anything for the first time"—says a lot about the weakness of the case against e-cigarettes, which is essentially an emotional reaction against a product that looks too much like a long-reviled symbol of evil. "Part of the furniture for us is that the tobacco industry is evil and everything they do has to be opposed," University of Nottingham epidemiologist John Britton tells the Times. "But one doesn't want that to get in the way of public health."