But there’s a powerful group working against this innovation — and it’s not Big Tobacco. It’s a coalition of government officials and antismoking groups who have been warning about the dangers of e-cigarettes and trying to ban their sale.

The controversy is part of a long-running philosophical debate about public health policy, but with an odd role reversal. In the past, conservatives have leaned toward “abstinence only” policies for dealing with problems like teenage pregnancy and heroin addiction, while liberals have been open to “harm reduction” strategies like encouraging birth control and dispensing methadone.

When it comes to nicotine, though, the abstinence forces tend to be more liberal, including Democratic officials at the state and national level who have been trying to stop the sale of e-cigarettes and ban their use in smoke-free places. They’ve argued that smokers who want an alternative source of nicotine should use only thoroughly tested products like Nicorette gum and prescription patches — and use them only briefly, as a way to get off nicotine altogether.

The Food and Drug Administration tried to stop the sale of e-cigarettes by treating them as a “drug delivery device” that could not be marketed until its safety and efficacy could be demonstrated in clinical trials. The agency was backed by the American Cancer Society, the American Heart Association, Action on Smoking and Health, and the Center for Tobacco-Free Kids.

The prohibitionists lost that battle last year, when the F.D.A. was overruled in court, but they’ve continued the fight by publicizing the supposed perils of e-cigarettes. They argue that the devices, like smokeless tobacco, reduce the incentive for people to quit nicotine and could also be a “gateway” for young people and nonsmokers to become nicotine addicts. And they cite an F.D.A. warning that several chemicals in the vapor of e-cigarettes may be “harmful” and “toxic.” But the agency has never presented evidence that the trace amounts actually cause any harm, and it has neglected to mention that similar traces of these chemicals have been found in other F.D.A.-approved products, including nicotine patches and gum. The agency’s methodology and warnings have been lambasted in scientific journals by Dr. Polosa and other researchers, including Brad Rodu, a professor of medicine at the University of Louisville in Kentucky.